Both Python versions have reached end of life for nearly a year or more. Tooling starts to be problematic for them, for example, GitHub Actions for Python 3.4 seems to be broken. Python 3.5 was problematic typing-wise, because it added the typing module in a minor version, so it's hard to test it.

Old versions of typing_extensions remain available. This means t hat users of obsolete versions can't use newer typing features, but I think that's a reasonable tradeoff.