SQL is common for ETL because typically at least one, sometimes both, ends of an ETL operation is an RDBMS for which SQL is the standard language. It has nothing to do with lack of brittleness.
They weren’t.
I guarantee you, before either of those existed, when Data Warehousing was often done with a different version/configuration of the same brand of RDBMS as the transactional store (the latter likely using something closer to a normalized schema, the former using a star or snowflake schema), using SQL for ETL was absolutely normal.
Which is why newer data warehousing / data lake systems support SQL even though they aren’t RDBMSs: a couple decades of RDBMS dominance made it the JavaScript of data storage.
> Because it’s not a general-purpose imperative loosely typed brittle language like Python.
Its not general-purpose or imperative, its just as much “loosely typed” as Python (both Python and SQL are strongly typed.)
Its not clear what concrete meaning “brittle” is supposed to have in this claim, so I can’t evaluate its accuracy.