Well, there aren't reasons why Python couldn't have that, but there certainly are good reasons why the Python maintainers decided that type of runtime was not appropriate for that specific language--not least among them that maintaining a scheduling/pre-empting runtime (which is the only approach I'm aware of that works here without basically making Python into an entirely unrelated language) is very labor intensive! There's a reason there aren't usable alternative implementations of ERTS/BEAM, and a reason why gccgo is maintained in fits and starts, and why the Python GIL has been around for so long. Getting that type of system right is very, very hard.
> maintaining a scheduling/pre-empting runtime (which is the only approach I'm aware of that works here without basically making Python into an entirely unrelated language) is very labor intensive! There's a reason there aren't usable alternative implementations of ERTS/BEAM […]
You seem to know a lot about PL. Could you elaborate on that reason and on the maintenance burden of a preemptive runtime?