An interesting deep dive on why this is the case (from 2015), in case anyone wants to know more:
http://techspot.zzzeek.org/2015/02/15/asynchronous-python-an...
http://techspot.zzzeek.org/2015/02/15/asynchronous-python-an...
https://github.com/MagicStack/asyncpg
They're both incredibly experienced developers, and I don't have any good steer on the discrepancy.
Would love to see some independent benchmarking on a typical use case to get a clearer picture on how valuable (or not) asyncio is for high-throughput database operations.