I think the python maintainers are still feeling burnt by the consequences of the "batteries included" approach from the old times.
I still hear people complain about how such and such removal between "minor versions" of Python 3 (you really should be thinking of them as major versions nowadays — "Python 3 is the brand", the saying goes now), where they were warned like two years in advance about individual functions, supposedly caused a huge problem for them. It's hard for me to reconcile with the rhetoric I've heard in internal discussions; they're so worried in general about possible theoretical compatibility breaks that it seems impossible to change anything.