EzekielRaiden
Follower of the Way
Rats are associated with plague, death, ugliness, trash, etc. They're wonderful animals as pets, but wild rats have a very bad rep. That alone means a lot of people have no interest.I'm not convinced that werewolves actually fill the niche, though it's not a terrible working hypothesis. Might explain why rat-based races are also scarce in D&D outside of 3e OA and nezumi. Though why weretigers wouldn't similarly suppress Tabaxi becomes a question.
And for canid races - we did have dog hengeyokai back in the days of OA - as well as a few other shape changing animal forms.
Also, IMO, hengeyokai are just a cultural variation of werewolves. They're shape shifter people, some of whom happen to be dog/wolf/fox type.
Like I said, the werewolf (specifically wolf) is just...a presence. It spreads to cultures that don't have it distinctly (see the Japanese love of exploiting and reinterpreting Europen werewolf stories). It's an archetype and a dozen potential dichotomies or open questions all balled up together.