Geez, you're right...why are there so few mothers around in Ranma?

Becasue the mothers in Urusei Yatsura and Maison Ikkoku were, for the
most part, utterly awful.  Indeed, Ran's mother is my vote for the
most abusive parent in anime.

--Sean Gaffney
--Akari and Ryouga!  Ryouga and Akari!  (Sorry, Andrew)