they rejected the request of Deep Rock Galatic and Dwarf Fortress to add a dwarf tag, the two teamed up on a co marketing campaign to get the decision reversed, Steam acquiesced.
As far as I've gathered Valve "accidentally" created the elf tag instead when the dwarf tag campaign happened. When someone noticed they went "oh, whoopsie, hehe" and added the dwarf tag too. So elf should also be a tag now.