I work on a team that has some old projects in python that we're gradually deprecating. A major one is stuck on 3.7 because 3.8 added automatic async mocking (which is great!), but this broke the existing third-party async mocking framework and it's never been updated to be compatible with newer Python versions. So we'd have to invest time in porting all the tests from the 3rd-party framework to the standard library, but it's not worth it because we're hoping to deprecate the whole project soon anyway.