I suppose it also just has to do with their different styles. In Jazz 1 wasn't it Nick Stadler who animated those cutscenes? While in Jazz 2, it was Noogy. And as expected from Noogy's designs, Jazz looks alot more buff and serious in his version. While in Stadler's version Jazz reminded more of Bugs Bunny.

So yeah, I guess that's it. I feel they were slightly going in the right direction, but like you said, it's not quite the same.