SM uses quite a few "recolored" trainer classes which is basically the same model of another trainer class with some accesory. For example

Beauty with a golf club is a golfer
Lass or Youngster with some sport accesories are young athletes
Skull grunts without masks and chains are punks

And yet there's quite a few human models that were never used as trainer classes the woman who's model was used for Hapus Grandma (she's all over alola) or the guy with Blue shirt from Hauoli or the girl that teaches you how to greet in Alola. There's more than that.

So why being so cheap in using the same model for different trainer classes when some models were never used at all but they're there?