I've always wondered this, why Honda designed the CB/CL175 and 200 as twins and not singles.
Sorry for reviving this topic, couldn't help myself, but here we go:
It's all about the market. Honda (and to be fair, many others) never thought that singles would sell in the US (other than dirt bikes and that kind of thing). Even Suzuki never imported their DR BIG (aka DR800) to the US.
As with many of these questions long after the fact, Honda didn't say much over the years as to why they did many of the things they did.
It still boggles my mind why they ever went with a 360 crankshaft on the 400/450s. The british competition was pretty much done at that point, they always used 2 carburetors, so no benefit from making it cheaper with only one, and the balance shafts also never helped. I just think they did it because they could, just for the kick of it at this point.
And boy, am I glad.
But they never sent a single cylinder street bike larger than 125 to the US AFAIK (none are shown in the US Honda ID Guide).
Bingo.
99% of the bikes we ever got here in Brazil were the most simple bikes possible, it's what worked for the market, and well... 50+ years later, it still is, but at least now we get overhead cams.
Lemme put down a brief history of the most sold bikes (who detains literally more than 50% of the market), the "Honda CGs", hope you guys can enjoy this.
1976-1982 CG125 - derived from the CB125. Also the first bike ever produced by Honda here in Brazil.

Not much to talk about it, what you see is what you get, except that it wasn't an overhead cam engine, but an overhead valve engine with pushrods.
On 1981 they also released what as far as I know is the first (production) bike to run on ethanol on that same engine, bike became popularly known as "CG Pelé"

I'm sure you guys understand why.
1983 - 1988 - The "New" CG 125

Not many changes. To note is the new carburetor with the "Ecco" system, which I never managed to figure out what it was, probably just a leaner mixture, but the bike was more efficient and did more mpg. In 1985, it got 5 gears (finally).
On the styling changes, the bike resembled quite a bit the first few Brazilian CB400's - Which kind of looked like your 1970's CB400T's but less Custom and more Naked.
There was also a "Cargo" model, meant for delivery work, main change being a metal structure on the back of the bike to do delivery work, the "Cargo" model kept existing on almost every single generation as well.
Just for additional context: up until this point where the imports were closed, Yamaha's response was the RD135, which, of course, being a 2 stroke, completely obliterated the CGs when it came to speed, but 2 strokes being 2 strokes... Maintenance, noise, smoke and oil smell. (but also fun).
1989 - 1993 - CG 125 "Today"

Sturdier frame, first CDI model (that's why it carried the "Today" name") and lots of styling changes. The bike resembled quite a lot the CB 450 DX, which had JUST started to lose its shine after the imports were opened again in 1989 (when the CBX 750F arrived, along with the RD350's).
74 changes to the frame, 69 changes to the engine, but still a pushrod, workhorse of a thing.
All of these engines were known to be built like a freaking tank, barely required any oil (or oil changes).
I never understood why the round gauges/etc with a square headlight, though.
1994-1999 - CG 125 Titan

Few changes to the engine, sturdier clutch, but still a pushrod one, big changes to its appearance. They rounded out everything.
This one is also known as a freaking tank and if you ride in a city in Brazil, you're bound to see it. The right side o-ring leaks are common, though (although, easily fixable)
2000-2003 - 5th gen CG125.

They finally rounded out everything, and added electric start to some models. The top of the line ES model (not pictured here), got electric start and a front disc brake.
To me, the best looking one to this day. They also released the CBX250 Twister right around the same time.
2004 - 2009 - CG 150 Titan / Sport + CG 125 Fan

They introduced the 150cc model which finally was updated with overhead cams. They kept the 125 engine though, on the cheaper model, "Fan".
Also known as a tank horse, I've seen these bikes be overbored to 200cc's and run just fine on everyday use and even delivery work.
Competition engines are modified to run on more than 310cc's and methanol, to this day the number 1 engine for that.
The "Sport" model had a few apperance changes (mainly a silver side cover), with more agressive cams and just a tad more torque and HP.
2009 - 2013 - CG 150 "Titan Mix"

If not for the Speed Triple, this would be the worst looking headlight I've ever seen on a bike. It looks so much worse in person.
They kept the 150 engine but fuel injected it, and they kept a separate 125 engine for the CG125 Fan, although they updated it to be OHC as well.
The tail of this bike though... The sexiest the CG ever got, imo.
In 2013 they once again updated the appearances, added CBS and created yet another model - The Start model (which used two drum brakes) was also introduced.
2015 - 2024 - CG 160

Lots of styling changes.
A new engine, which is also the same one you see on a bunch of international models like the CB190, caracterized by its very small head cap.
This engine, though... Kind of noisy around the head, not nearly as strong as the 150's when it comes to reliability or modifications.
They updated it in 2025, main changes include LEDs, FINALLY an aluminum swingarm and a disc brake in the back (although the rear disc brake is only for the top of the line CG Titan).
These bikes have become stupid expensive with the stupid economy/politics and the fact that... Well,
a Honda is a Honda and I don't think there's anywhere in the world where this applies more than Brazil.
For context, this is the top 15 most sold bikes in Brazil in 2024, by month, total in the right side.

You can see how Honda CGs basically sell more than most of the other bikes combined.
Every single one of the bikes in the top 15 is a single cylinder bike, the only water cooled one is the PCX 160 (which is a scooter, so justified).
A brand new CG 160 costs around R$24k brand new. For context, an Yamaha Factor 150 costs R$17k (but costs more to maintain
[because it's not a Honda], and is marginally slower).
You can get an old CB450 for around R$14k (and that's also way too high, less than 3 years ago they would cost around 8 thousand).
Other few notable singles I'd advise you guys to research if you're interested in Honda singles:
Biz 125 (C100 / 110 / 125) - Absurd workhorse of a Cub.
Runs without oil, runs with cooking oil, probably runs with vodka in the tank (I've seen videos of older models running with freaking Alcohol from a pharmacy), doesn't even have a clutch, just freaking runs, doesn't care about the pavement, doesn't care about suspension maintenance, or any maintenance at all for the matter. It is the Brazilian daughter of the C100 Dream, and in my opinion surpasses it. Same goes for the Pop 110i (which uses the old Biz 110 engine), but the Pop does have a clutch.
NX350 Sahara - 350cc RFVC motor - Ever wondered what would happen if you took the XL 350 and made it into a tourer? Well, look it up! This bike looks absolutely amazing to me and is a staple of the 90's, especially with its colors.
NX400 Falcon - 400cc RFVC motor, street bike but still quite high from the ground. To this day, people riding 600cc 4 cylinder bikes in big cities run away when they see a Falcon as it's still used by thiefs because of it's ridiculous torque and agility - For some reason, though, they removed the oil radiator/cooler from the 350's, so the Falcon suffers from overheating in certain conditions.
CBX200 Strada - Same engine as the XR200R - I don't know about its reputation back then, but nowadays it's known as quite troublesome. Even the dirt bike guys don't really like the XR200's anymore because of that.
CBX250 Twister - Exported as CBF 250 - DOHC Air cooled 250cc engine - Marked an entire generation, very strong engine, AWESOME (in my opinion) looks.
Gave birth to the fuel injected CB300R as well, which unfortunately had a chronic problem and would crack heads left and right. After a few years Honda changed the head design and moved the spark plug position along with using a smaller one, it didn't completely fix the problem, but helped. Despite its problems, the bike is stupidly fast (when not at the mechanic).