I feel like the Rebellion-turned-Republic would have a slight issue with using technology and equipment that was so galactically identified with oppression, enslavement, and brutality.

I feel like the end of the Empire was a bit akin to the de-nazification of Germany after World War II. The incoming regime would probably want to distance themselves from their predecessor as much as possible in order to present a new face to the galaxy that wasn’t connected to the evils of the Empire. The Rebels tromping around in AT-ATs would be a bit like the Bundeswehr driving around in Tigers.