The problem with a lot of the other mascots (bar Pikachu of course) is that they're a bit too one note, doing mostly ONLY the baby role or ONLY the comic relief role, and if anything often portrayed as useless in action outside the handful of 'hidden badass' moments any dead weight character is entitled to in the show.
It probably doesn't help that the writers think main girls have to have a cute plush or baby-type pokemon to appeal to girls. It's probably a culture thing in Japan, female characters get mostly cute pokemon, and whoever their main pokemon is, is treated like a baby or constantly held in the main girls arms to cuddle, etc.