One of the key issues in Omaha 8/b is that you always want to have more than two cards working. In fact, the only hand you could justify playing out of any position where you only know two of your cards would be one that contains A2. When your hand is not playing at all for low this becomes more important. When you are playing a hand with only high features all four of your cards need to be working. What I mean by this is that all four of your cards have to be related to each other in some way.
If you are playing big pairs (by this I mean any pair 99 and above) the other two cards need to be strongly related to the pair. So, K K T 3 is a completely unplayable hand. You have exactly two kings, a hanging three unrelated to any of the other cards and no suited cards that would give you a flush feature. The only flop you would truly be happy with is one that gives you Kings full. This is a hand that if you were raised in the big blind you could throw it away. Certainly you would never call a raise with this hand in the small blind.
As a contrast consider K K 2 3. This is an incredibly powerful hand, one that you could play out of any position at the table. You have two suits, spades and diamonds, you have a big pair, kings, and you have two relatively strong low cards, 23. You are playing for high and low and have multiple high features to your hand. Plus, when an ace hits the board, you will often still have the nut low draw (as in a board of A 4 T) and you might often have the nut flush draw also (A T 4). You can flop many powerful hands with this and it is a hand that is easy to get away from. If the board is 2 5 6 for example you have an easy fold.
As another contrast, consider hands like Q Q J T and J T T 9. Again these two hands are eminently playable because all four of your cards are strongly related. Further, when you make your hand you will almost always be getting the whole pot as flopping these hands well generally means high cards will hit the board. You have lots of straight possibilities. It is easy to flop a high wrap-a very powerful Omaha hand. If the board hits with a 98K, for example, and you have QQJT you can make a straight with a 7, T, J or Q. This is called a total wrap, when any of four possible cards makes your straight. Further, when you make your hand with the Q this also gives you a set so that when the board pairs you still have a very powerful hand.
So big pairs can be very powerful starting hands but only if you have two strongly related other cards in your hand as well.