> I think this seems a pretty insane way of doing it; why not change the default behavior instead of making another driver with a separate name as well as keeping the old one too?

Because, as they clearly explain in their rationale, that would break compatibility with all of the existing software out there that relies on the current semantics.

Thou Shalt Not Break Working Code is the first rule of building software that other software relies on.

They're deprecating but retaining the old driver to give people a transition period in which to modify their software instead of kicking them in the teeth immediately or forcing them to hold off on upgrading. That's the mature approach to fixing mistakes that people nonetheless built assumptions around.