Could be probably less be a due to the little girls and more due to the parents part of the target demographic not wanting their girls to play with "scary sea monsters". ( Keep in mind that even Monster High is strongly humanized to the point that the main difference between the ones based on Nessie and the Creatue from the Black Lagoon is that the Nessie one has a tail and red hair The dude is supposed to be yet another a different type of sea monster )