Because of werewolves.
Not even joking. Werewolves take the wind out of the sails for any canine-like race. And you don't have to look far to see this in gaming, either.
Elder Scrolls? No dog-people, but there are werewolves, tied to Hircine, Daedric Prince of the Hunt.
World of Warcraft? I mean, there's fox-people, but the actual canine race...are literally werewolves. They even have a human form.
Eberron has Shifters, but they're only weakly animal-like...and guess what, they canonically get mistaken for werewolves!
Werewolves are simply such a presence that there's really nothing else that can challenge them. Frankly, I wouldn't be surprised if "werewolf" actually becomes a race in 6e or 7e. WotC is trying to capture the animal-person thing with their new race that I can't remember the name of, but I'm not sure it's gonna stick.
And the thing is, the only other proper canine besides wolves would be dogs, which has...unfortunate implications.