[geokon]

not a native chinese speaker, but couldnt this have to do more with requiring qualifiers?

There seems to be a very strong preferrence to adding qualifiers, especially to single character words. And 不 is just one of them

很好 (very good) is strongly preferred to just a plain 好 (good). similarly youre seldom going to just say 錯 差 or 行.

So if you want to say good, and not verrryyy good, youre left with "not bad" 不錯

it still holds for 2 character words. i was told that just saying 無聊 (boring) can have a very rude conotation, though i dont quite understand the subtext (maybe someone can elucidate). But if you say 很無聊 (very boring) it weirdly enough sounds better

unqualified words as far as i understand also often look archaic. tied to the preference for 2 character words vs 1 character words (my guess is bc classical chinese is written and its hard to make out a single character word with tone when speaking)

hopefully a native speaker can weight in...