Why do the level 90 beast tribe only require level 80 crafters.

[Raskbuck]

Because the beast tribes have, and always will only be a leveling activity.

It was a leveling activity in ARR.
It was a leveling activity in HW.
It was a leveling activity in SB.
It was a leveling activity in ShB.

They are 'endgame' unlocks for the purposes of levelling.

My memory might be failing me, but I don't recall being able to use Trained Eye on the Dwarves dailies. Not that it really matters, anyway. It's all super trivial.