I think
Bella is ugly, and
Belle is even uglier. It's such a 19th-century whorehouse madam or milk cow name.
Maybelle is very hillbilly, stereotypically so.
Mabel is stereotypically a worn-down, toothpick-chewing waitress name, and
Belle doesn't make very much sense as a middle name for it because the bel in
Mabel isn't pronounced like
Belle.