Right now there are close to 400 pending pull request on Github. Pending requests for simple bug fixes like this are almost 2 years old without any real updates.
I know pull requests often are complex, and the discussion back and forth with the contributor takes time.

Having that many many pending pull requests creates the feeling that you don't really want them. Especially since they are almost never updated other than when they are rejected or merged.
This is not necessary true, but seeing the wall of pending pull requests for a first time contributor is really discouraging.

You have a big community of talented people that wants to help out. Let them.