The writing surrounding Eden is all kinds of weird, frankly. None of the characters who should know about it acknowledge its existence until the raid questline starts. By that point every character who knows is either dead or presumed dead, leaving Urianger to be the sole source of exposition on its history—when he should be just as in the dark as everyone else—for most of the raid questline's runtime.

I can't say I'd hold it against Emet-Selch for not thinking to check that out because of that. 'cause otherwise, I'd also have to hold it against Ardbert for wasting time talking about his feelings the whole time instead of warning us about the city-sized sin eater that caused the Flood of Light. Or Minfilia for spouting off cryptic spoilers as foreshadowing instead of offering advice that'd actually be useful re: the aforementioned world-ending abomination sleeping in her backyard that she arm wrestled into unconsciousness.