I'm not familiar with the Python client specifically, but Redis clients generally multiplex concurrent requests onto a single connection per Redis server. That necessitates some queueing.

Redis latency is around 1ms including network round trip for most operations. In a single threaded context, waiting on that would limit you to around 1000 operations per second. Redis clients improve throughput by doing pipelining, so a bunch of calls are batched up to minimize network roundtrips. This becomes more complicated in the context of redis-cluster, because calls targeting different keys are dispatched to different cache nodes and will complete in an unpredictable order, and additional client side logic is needed to accumulate the responses and dispatch them back to the appropiate caller.