Uhm… and why does the user have to transition to snaps?
They don't. But Canonical will no longer be providing debs in primary Ubuntu repositories, so those transitional packages exist so that users don't wind up with an abandoned, old version of Firefox.
Why does Canonical provide those transitional packages while there are perfectly valid debs for the same thing?
For the same reason neither Ubuntu nor Debian provide debs for Google Chrome, despite Google having an official apt repository? Those debs exist in somebody else's apt repository. If you want to add that apt repository, you're welcome to. But those external packages aren't part of the system they provide.
you instantly refute yourself, kudos!
Your unwillingness to accept what I'm saying doesn't make what I'm saying contradictory.