Expert dungeons generally have the same ilvl requirements. ARF has a lower check (and if it had rewards, less valuable loot), thus it would be considered "too easy" for an expert label.
They could have easily upped its ilvl to the same as the EX dungeons (they already aren't much different), give it some esos, and put in some actual loot into the dungeon if they thought people would care about that (although given how most Valerian stuff goes to the floor nowadays, I'd imagine they wouldn't)

Really, this is a problem they should have foreseen.