[NooBliss]

Yep. Not to mention that R'Lyeh Illithids actually remind of lovecraftian Deep Ones much more than Atlanteans. Ironically, yes.
Think of it - Illithids are sinister, reclusive underwater beings that serve some ancient otherwordly evil, plot and inspire cults etc etc, just like lovecraftean Deap Ones.
Whereas Atlanteans are just a race of fishlike beings who simply live there, underwater. Well, perhaps there was something special about them in EA, with that weird orb and the terrible secret of Deep One mages, but it died with them. In MA, when Atlanteans interact with humanity, they are just soothingly mundane aquatic humanoids.