Realistically, any practical argument for Python's lack of block scope is probably just sour grapes. The real reason, I'm guessing, is that it started out as a hobby project 30+ years ago, and that block scope is not something GvR personally felt was worth the effort to implement at the time.

Followed by three decades of not wanting to do that particular breaking change, because doing so would be far more painful than anything that happened in Python 3.0.