I was of the thinking, and everyone I know was as well, that Jabba was not meant to be able to move very well. Hence his state in ROTJ. I believe the only reason he suddenly became mobile in 1997 is because there was no other way to make the scene work. Not that it worked very well anyway, but that's why. They did consider putting him on a very thing hover plate, with a sort of curved little railing at the bottom holding Jabba's belly in. I would have prefered that, if only because it would have maintained his natural immobility. And it also might have enable Jabba to spin around and remain face to face as Han walks around behind him.

But no, they went for the catastrophe we saw in 1997.