I worked in an org at Yahoo that required all development to use Atomic, and that was essentially the reasoning as presented. The Atomic authors put a lot of effort [1] put into proving the size point, enough that it was pretty difficult to argue with. The stylistic issues were sort of swept aside; less size == faster page loads == more revenue.

If you believe the size argument, and care more about short term revenue over developer productivity or happiness, it makes sense, I guess.

[1] https://acss.io/frequently-asked-questions.html#what-are-the...

> Why didn't they just use css as intended

Too many engineers and not enough actual problems.