I've gotta disagree with you here - it's not uncommon for me to be diving into a library I'm using at work, find a small issue or something that could be improved (measurably, not stylistically), and open a PR to fix it. No big rewrites or anything crazy, but it would definitely fit the definition of "drive by change" that _thus far_ has been welcomed.

>find a small issue

>No big rewrites or anything crazy

I think those are the key points why they've been welcomed.