Maybe certain name orders just sounded right when they were writing the muppet show. Cettain combinations of sounds work better than other. Ther softer Waldorf sounds better after the sharper Statler. Same as Bert and Ernie. Ernie is a little sharp, but not as much as Bert.
Bunsen and Beaker don't really follow this, but in this case the names aren't part of their act, ya know? Like Bert and Ernie are famous for their names and it became kind of a joke, but the name placement doesn't really matter with Bunsen and Beaker. Or does it? I just don't know.