I don't use either but think I understand the historical difference:
Nakiri dates to a time when the Japanese diet at home was mainly whole fish and vegetables.
The two knives required were a deba and a nakiri.
I think usubas were more for professional kitchens.
There's some background in this post on the history of Japanese knife types:
https://cheftalk.com/threads/some-basics-on-japanese-knife-history-long.56934/
Assuming this is accurate (I don't have other sources), the important distinction here with Japanese vs. Chinese traditions are that early Japanese knives were either designed for vegetables (nakiri/usuba) or for fish (deba). No such thing as a general-purpose knife for both veg and protein. In fact, for a long time you weren't officially supposed to eat any meat or fish at all, although a lot of that was going on anyway, when it was available.
Chinese had a more diverse diet in terms of meat and poultry, so they use the Chinese cleaver for everything.
I'm not sure the diet was more diverse, although it would vary by region. China is huge, and naturally you get more seafood near the coasts, some river fish inland, and then beef up in the Muslim Northwest. What I've read of the history of Chinese cuisine is that meat was available but in small quantities, often seasonal or only for special celebrations. At any rate, they didn't have the cultural proscription in Japan against having two different knives for veg and protein that should never be mixed. So one big cleaver in both thin and thicker versions was the traditional knife for home and restaurant kitchens.
What I don't understand is why a Chinese cleaver is considered so effective at meat and fish whereas the nakiri is considered useless for anything other than vegetables.
Personal opinion here -- there isn't just one way to cut up meat and fish. The
shape of a nakiri works fine if you're vertical chopping a pile of pork into mince, which is a major ingredient in Chinese cooking. But that works even better if the blade is larger and heavier, like a Chinese cleaver. It's why I bought two cheap Chinese cleavers just for that one thing -- chopping pork.
However, in my experience it's better to have a smaller, narrower blade when draw-slicing horizontally to butterfly chicken breasts, or filleting and de-skinning fish, that sort of thing. It's about surface drag. A narrow blade with less surface area than a nakiri or Chinese cleaver slides more easily through soft protein. So I don't use a nakiri for that, I use a long petty/mini-suji.
You
could do this with a Chinese cleaver, you'd just have more drag from the larger surface area. I think it's worth noting that these operations like butterflying chicken or skinning fish aren't a typical form of Chinese food prep for meat and fish. The amounts of meat are small, cut in small pieces or chopped, and fish is often cooked whole without removing the skin. The cleaver works in Chinese cuisine because the knife and the dishes have co-evolved together.