Because there's nothing 'furry' about elves.
When it's human/elf, it's basically 'human + human with pointy ears'.
For example: https://e621.net/posts/4950231
What's 'furry' about that? It's human + exotic human.
And, to expand on that: Orcs + humans or elves is yet more non-furry content.
It's 'human with green skin (And sometimes an underbite) + human (or elf)'.
Example: https://e621.net/posts/4948020
Not furry in the slightest.
Ain't e621 supposed to be about collecting furry art? Why is art lacking furries of any kind allowed?
Orks? Not a furry creature.
Elves? Not a furry creature.
So why is art where the content is only these non-furry beings allowed?