The overhead of working out where the people who maintain the code are is usually higher than just fixing the bug I found. This is doubly true if the bug is bad enough that I need to temporarily fork the repo to deal with it.
In the same way that the maintainers don't have an obligation to review my PR, I don't have an obligation to go find them and learn how to use IRC/bugzilla/mattermost/mailing lists/smoke signals/yodelling to communicate with them with the exact secret handshake to get a review. I can just throw a PR out there, point our code at my fork, rebase it whenever they make changes, and otherwise ignore their requirements until they either fix the bug themselves or merge my code.