This thread may likely be closed if the Moderators and GTPlanet public have their way.
In the same sense, you may as well ask why there weren't any drag racing in GT2? Another situation is "if there is no drifting and there are drifting cars, are they still race cars?" You damned right they are. Maybe not Le Mans or 24h at Nurburgring race cars, but nice ones nonetheless. If you can't drift on asphalt, but you can always go into opposite lock in rally.
But on a positive note, don't give up on hope for drifting in GT4. No really, I'm serious. Just hope that GT4 has much better execution and actual use for cars in GT4 than in GT2.