And why should they re-write the entire world? It's just a wrapper library to openssl and it was marketed heavily to the community (at the beginning) as one where maintainers would follow good practices and not try to write security-sensitive code as they are not security experts, but just rely on openssl so that all focus go into the same place.

So either that's still valid (and not too much of rust will come in to make a real difference security-wise) or they have revisited their position and will re-implement a bunch of openssl logic (in rust apparently though, and not in Python as it would be more logical, and as golang does successfully). And in the latter case, why just not focus on wrapping rustls instead?

In either case, the hand is being forced: it's a small amount, and I don't see how it would have been an excessive burden to maintain such a small logic as an opt in for a period. It makes much more sense to read this as a move to forcefully push rust into the python ecosystem.