I think it was more about somewhat giving some hindrance to DTing. You have like every other advantage whenever you DT: your health recovers ridiculously fast, your attack power seems to double, and the enemies go into slow motion. Only now you have to go up into the air and deal the damage, likely with your weaker angel or rebellion weapons. If they didn't float into the air, you could much more easily wreck the crap out of them with your somewhat ground based, high damage demon weapons. As is, when I DT I yank down the strongest jerk and proceed to Trinity Smash it's face in.