Yes. It’s difficult to get developers on other teams to even look at unsolicited pull requests. (The open source world is a different story.) I’ve written extracurricular but unambiguous improvements to my own team’s code, and only the tiny ones have been reviewed.
Discussion
I've almost done it a few times; write it up and then don't submit.
These days I try to resist even doing the work, because it’s almost always wasted effort.
