And in my experience, submitting a well-reasoned, simple pull request to add a small change or fix a bug always results in a merge.
As someone who also maintains a few (much, much smaller) OSS projects on GitHub, I really understand the 'no' mentality. It's often much harder to say no, but usually I try to put it in a positive way (yes, this is a worthwhile idea, yes, it looks like it could help in this situation, but no, I won't be merging it because I don't think most of the project's users would benefit from its inclusion).
Part of the difficulty comes from the dynamic changes of GitHub. 10 years ago, usually folks would discuss a change prior to submitting code.
Now, it's more common for someone to assume code is wanted, and then it's easy to be a little disappointed when you find an upstream would want it implement differently.
In all though, GitHub has done wonders for standardizing contribution processes.
As someone who also maintains a few (much, much smaller) OSS projects on GitHub, I really understand the 'no' mentality. It's often much harder to say no, but usually I try to put it in a positive way (yes, this is a worthwhile idea, yes, it looks like it could help in this situation, but no, I won't be merging it because I don't think most of the project's users would benefit from its inclusion).