[Yads]

It's the same reason you want to raise with good hands in holdem. You want to get your money in when you have the best of it. Do you ever slow play pocket rockets in holdem? No, because you have the best of it, so you want hands that do not have the best of it to put money in the pot. So why would you slowplay great hands in Omaha?
Omaha unlike holdem is more about preflop hand selection than it is about post flop play. Not sure if you agree with this, but whatever. So why not get your money in when you have by far the best of it, pre flop? Obviously you don't necessarily want to raise from early position just to end up heads up with a hand that has a good chance of beating you (like you pointed out). But if you can trap players that have already put in a bet with junk hands, why on earth would you not raise?