Before you would write a Java/c++ class that would do the map/reduce job for you distributed over 100s of CPUS. And you would feel like you were on the bleeding edge doing innovative stuff.
Turns out that SQL is a perfect API for map/reduce.
Everything you write in SQL can be transformed into a massively parallel job. And you don't even know about it.
This is the secret behind BigQuery and Trino/Presto/Athena.