I'd suggest they did that becuase one decent juggle could end the match and the whole violent combat would be out the window and it would be too much like Soul Calibur it would have been nice if the barriers dissapeared at the finish him screen so you could smack your opponent into oblivion.

because it would be fairly difficult
seems like a lot of programming

I too find it a shame that, with all that great stage design, they didn't give some stages more exploration capacity. I mean, Quan Chi's Fortress and Lin Kuei's arena would be great to go around. I mean, I understand barriers in stages like the Acid Bath, but next time, I would like to see some DoA-like stages, with real limits (walls, doors, rails even).