This. It's been this way for all 4 versions of TES and lore has stated that only 10 races inhabit Tamriel. Besides it's already been confirmed that all 10 races are returning,
This is actually counter to the truth. The truth is, it would complicate the game in story and possibly mechanics to add more races. It would make perfect sense within the lore, because there are other known races in Nirn aside from the ten that appear, and that is before you even commence dealings with the various races of immortal Daedra, who often find ways into Nirn despite all the injucntions against them. The Lore strongly supports more races. . . the devs probably do not. :brokencomputer: