The project owner could of course just write “No” without any explanation, but most projects I’ve seen that don’t take PRs have a reason for it: they prefer patches by mailing list, or don’t accept contributions but have a forum where you can post patches, or are a mirror of an upstream you should contribute to instead, or whatever. Usually this information is in the readme, or a wiki somewhere, or an automated PR-closing bot; but it would be a lot easier all round if GitHub let you replace the PR tab with some text so there was a consistent place to look for this information.

-Nobody- cares if your lonesome project is not accepting PR or even better stands denuded of any pretense of README, etc. For these it is sufficient to have a OSS license named and you’re good to go. And if you ignore PRs — and you are under no obligations to do this imho — no one will post to HN to tattle on you, because:

All these discussions are about ~hot properties. Implicit in all this is ego, prestige, and potential for profits, that is ownership, attribution, and control of some kind. You see the same dynamics apply at the next level of OSS projects hitting pay dirt ($) and locking horns with Cloud providers and ‘modifying’ OSS licenses.