This has been a problem for like 20 years and they have refused fixes before. And there have been fixes. They just don't see this as important
it's practically a religion that its a thing they wont change
"To be clear, Sam’s basic approach is a bit slower for single-threaded code, and he admits that. But to sweeten the pot he has also applied a bunch of unrelated speedups that make it faster in general, so that overall it’s always a win. But presumably we could upstream the latter easily, separately from the GIL-freeing part."
[1] https://mail.python.org/archives/list/python-dev@python.org/...
A lot of that is stuff that is enabled by, or was blocked pending, the new parser; I don't think it was blocked on Guido, and Guido haa hardly stopped being active and influential since stepping down as BDfL