Apparently these patterns are from PEP 639: PEP 639 – Improving License Clarity with Better Package Metadata | peps.python.org. Unfortunately, it doesn’t really seem to include a rationale for such a narrow definition of glob.
Looking at the linked discussion, @konstin seems to have authored the latest version: PEP 639, Round 3: Improving license clarity with better package metadata - #72 by konstin. You seem to have authored the earlier version per PEP 639: Incorporate the latest discussion feedback by befeleme · Pull Request #3866 · python/peps · GitHub.
The earlier version was specifically talking of “portability”. On one hand, spaces are traditionally known to cause problems with badly written code. On the other, I don’t think it really applies here.