> There is also the argument that it could "divide the community" as some C extensions may not be ported to the new ABI that the no GIL project will result in. However again I'm unconvinced by that, the Python community has been through worse (Python 3) and even asyncIO completely divides the community now.

I think the fact that you can name two other recent things which have divided the community is a solid argument for being a least a little gunshy about making big, breaking changes. There's the cost of the changes themselves, but there's also a cost to the language as a whole to add yet-another-upheaval.

Performance is important, but not breaking things is also important. I can understand the appeal of doing something suboptimal (but better than current) in favor of not introducing a bunch of harder to predict side effects, both in code and the community.