Because it's a niche? You don't need async for most stuff Python is used for, it's a "nice-to-have", and it's annoying to add. If you have to have concurrency/threading/etc, there are other languages with better paradigms.

The same thing happened with Perl and its weird threading (for different reasons, but still)... I guess Python didn't learn that lesson. Perl also gained async and coroutine support, but I think they were added a while after I left the community. I doubt many people use them today. Anyone used them and can comment on ease vs Python?

Async is perfectly fine for a medium-load single-threaded RPC/REST server wrangling. Ran it in production with 100s, sometimes 1000s of calls / sec with no issues. And thread-safety is much easier with async, where you know where the context switches are occuring.