Merging a PR by drive-by contributors is far from trivial. As the maintainer, you become responsible for the other person's code for all eternity; it's on you to read it, understand it, update it when stuff around it changes, and fix it when it breaks.

Not a problem for obviously-correct changes of a couple of lines, but most PRs aren't like that.

>and intentionally stifled improvement on xorg

Open source developers are not required to spend their time prioritizing your priorities. You just have to look to Xlibre to see that a lot of contributions are quite bad quality, and in a C codebase of Xorg's complexity and security profile it's not a small job to review things.