Distributed consensus + fsync() determines the lower bound on commit latency. We have to wait for the data to be durable on a quorum of transaction logs before returning success for a transaction. That's usually 5-10ms, even within a single region.
For user based keys, that sounds nice. Except on multiplayer cases, again in these cases one might find alternative solution rather than KV. I don't remember reading that any other service offers this speed.