My experience in the Python world is that the vast majority of projects only need one or two plugins for their linter, if any. Ruff has implemented so many flake8 plugins that I'm sure it has covered 99% of projects' linting setups.
In the JS ecosystem I've seen a fair share of custom rules developed internal to engineering orgs. Someone submits a PR a couple times with the same mistakes and it's easier to write a custom rule than it is to keep reminding them and possibly others to come.
