Thread pools are another variation on the theme. But if your threads block then your pool saturates and you can't process any more requests. So thread pools still need non-blocking operations to be efficient or you need more threads. If you have thread pools you also need a way of communicating with that pool. Maybe that exists in the framework and you don't worry about it as a developer. If you are managing a pool of threads then there's a fair amount of complexity to deal with.

I totally agree there are applications for which this is overkill and adds complexity. It's just a tool in the toolbox. Video games famously are just a single thread/main loop kind of application.