>>35422092Design.
Making a starter so explicitly feminine is going to turn off a LOT of boys the franchise does explicitly aim for, and for those who like it or willing to give it a shot, 87% male is going to ruin the immersion normies crave when playing - especially when GF seems to make it clear Primarina's canonically female (the Kukui/Hau Prims, Pokedex entry, Lana's Poppilo) but is too lazy to switch the starter gender ratio around for this thing.
It has strengths, to be sure. Strong plush sales and it's UU in Smogon, no easy feat in this day and age of broken meta. But even the plush sales and fanbase aspect is heavily tainted by the fact Japan may love idols, but in a pervy-skeevy way, or the inevitable manchildren wanting to fuck Prim (and if you're gonna claim on /vp/ such a fanbase is nonexistent, you're a fucking dumbass).
At least it's not Decidueye with all those expectations that poor thing had and managed to carve out a niche for itself compared to most other mons, even starters, out there.