If you spent the time and effort to hunt down the problem for them, the least they could do is look into it. repos that don't care enough are a waste of time.
TBF, even if your PR solves an actual issue a number of users have, it still might not be a good fit for the project's future, and starting a discussion about it might not be worth anyone's time.
More importantly, as you disclosed your solution, other affected by the issue can rely on your code in the meantime (= the rest of the project's life in some cases. I've been there). If it really is a critical issue that isn't solved, your fix can always be used in a different fork with better maintenance.
All in all, the upstream repo not responding to a PR isn't the end of the world I think, and the openness of the system makes it an acceptable state in many ways IMHO.
