If you do anything on the CPU or if you have any I/O which is not async you stall the event loop and everything grinds to a halt.
Imagine a program which needs to send heartbeats or data to a server in a short interval to show liveness, Kafka for example. Asyncio alone can't reliably do this, you need to take great care to not stall the event loop. You only have exactly one CPU core to work with, if you do work on the CPU you stall the event loop.
We see web frameworks built on asyncio but even simple API only applications constantly need to serialize data which is CPU-bound. These frameworks make no effort (and asyncio doesn't give us any tools) to protect the event loop from getting stalled by your code. They work great in simple benchmarks and for a few types of applications but you have to know the limits. And I feel that the general public does not know the limitations of asyncio, it wasn't made for building web frameworks on the async event loop. It was made for communicating with external services like databases and calling APIs.