What rengori said made sense, you hit overdrive/trance/whatever from taking a pounding, thus you would be pissed, and it would be weird to save that. Actually in IX steiner said that the trance was linked to a high surge of emotions or something like that.

Also the trance in IX just plain looks cool. In X it's just some flashy move, but in IX when you trance...you get all glowy and kickass.