>>43046374For what I've seen the Monstrous designs tend to be less popular than the Humanoid designs in general.
For example it's been pointed that Greninja, Primarina, and Inteleon are the only Water Starter Final Stages to beat out their pre-evos in popularity.
Note how Squirtle, Totodile, Mudkip, Piplup, and Oshawott are all more popular than their final stages but once you get to Greninja the tables suddenly turn?
Now also note how Greninja, Primarina, and Inteleon are also the only Water Starters with human characteristics?
My guess is fans just find humanoids more interesting?