This only happens because the file doesn't already adhere to the rules it's implementing. These are normally highly configurable, and once your code complies to a standard, the tool prevents future code from pulling you away from that standard.
> And sometimes, they actually insert bugs - string formatting errors are my favorite example.
Do you have a concrete example?
> Sometimes I'll get a pull request with like 2 lines of change and 120 lines of some reformating tool.
Is your existing code formatting at least consistent?
> You think I accept that?
This is a social issue rather than a technical one. You can tell people in your development readme to use specific style rules, or even a project-wide precommit hook. If your own code is formatted with one of these tools, you can even (to my understanding) set up automated checks on GitHub's side.
But of course you are free to reject any PR you want.