Mecheon
Sacabambaspis
I'd argue Goliaths have enough of a fan presence, which is why they're being PHB'd, but Goliath's advantage is they're half giants in everything but name and that's another very easy stereotype. The simpler a stereotype is, the more popular it ends up being as people know what to do with it, or how to go against theme to push at some of the odder sides of itNeither of whom have much of a setting presence in WotC circles.
Aasimar, they've tried to get at Tiefling levels but failed (even though, frankly, I think 5E is the best spot they've ever been in popularity wise). Which gave us the Aardling experiment