>>48039791I was just shitposting, but taking your topic seriously, the explanation has several aspects.
On one hand we have the case of Nurse Joy and Officer Jenny (and some more like Don George, the Cruise ship captains, and Vivian) who are a parody of the NPCs of various video games.
As a writer the resource of using doubles allows you to put your character in situations like; twins swap, prince and pauper, fish out of water, or simple script conveniences.
As an animator, recycling models accelerates the work in an incredible way, likewise for the voice department it is more practical to have few actors and not have to be subject to the agenda of a famous voice.
Now in-universe we could use your theory that due to great wars or the high mortality of the male population their genetic diversity is low.
I also like the one in which families like Jenny and Joy are humans with pokemon recessive genes (Considering that humans in this universe descend from a pokemon primate) making the females determine the phenotype of their offspring.
