Perhaps because the best hand in Omaha 8/b is AA23 double suited most players greatly overestimate the value of having AA in their hand. AA can make top set but Aces also play for low meaning that you are guaranteeing one piece to a low board when you flop a set. Because of this the aces have some of the same drawbacks as deuces through eights. Of course, being able to flop top set mitigates these drawbacks, but this still needs to be taken into account. Because of this, when you play AA you need to have some other feature to your hand-suited cards, other connecting low cards (AA34) or connecting high cards (AAKQ). A A 7 8 is actually a hand that you can throw away from early position and you should never call a raise with unless you are in the big blind. With this hand you have no good low features and no suits. The only feature is AA so really you are either hoping that your one pair will stand up, which rarely happens in Omaha 8/b, or that you will flop a set, which is a) less likely to stand up in Omaha 8/b than hold’em and b) increasing the likelihood that you are only gunning for half the pot by putting an Ace out there.
Unless you are raising out of steal position, limping in in the small blind or playing out of the big blind you should never play this hand.