Is there some particular reason to believe the Python team is even able to get good insight into regressions in the long tail of python packages?

Also it's important to remember that a lot of of material contributions to the community (either to the foundation, via jobs, or even open-sourcing part of their internal stack) might be coming from closed source in some way. It's not wise to ignore that & I think the core team is rightfully cognizant of needing to balance that (balance - not tip to one extreme or the other).