Or: Why can't you just merge my ten-line PR already?
I maintain over 200 open source projects. Apparently (this is news to me) I am ranked in the top 200 GitHub users by followers, and there are 18,000 forks and 42,000 stars across my repos.
On an average day, I see between 50-100 emails across my repositories for issues and pull requests, and I filter those down to about 5-10 that I deem worthy of a personal follow-up.
I merge between 5-10 Pull Requests per month, and commit new code or fixes around 166 times per month.
I'm one maintainer, in a tiny corner of the Internet, maintaining a small but broad set of projects from Ansible roles for infrastructure automation to a few small but still-used PHP and Node.js libraries.
Dealing with burnout
There have been a few times I've burned out. That's typical for many maintainers. You either learn coping strategies or burn out completely, and in the best case end up a woodworker or farmer. At least that's what I see most of the time.