I think the OP's explanation is the real one, but I still like to think this is a thing where more than one thing can be true

Western countries (USA) often have rich economies, which means that the average person in said countries often has better access to high amounts of storage than people from impoverished countries. This makes it so it's not a priority for companies targeting that audience to optimize for disk space.

TLDR: Rich countries get beefy PCs, which get unoptimized games

We like our apps to match our waists xD