I actually think it was just a way to showcase some "cool" (in Lucas's opinion) aliens. In From Star Wars to Jedi, you can hear Lucas talking about how with high production values and more experience, he could have made a much better ANH; well, we know where that went... Anyway, I think that Lucas may have subconsciously tried to make ROTJ a better ANH by relying on more effects. For example, they have many parallels. ROTJ and ANH both feature a grand battle with a Death Star blowing up. In both, there is a lightsaber battle. They contain Luke experiencing a revelation early in the film as opposed to later like in ESB. In ANH, Luke learns his father was a Jedi; in ROTJ, he realizes Leia is his sister. In my opinion, this Max Rebo sequence was George Lucas's way of trying to improve on the cantina scene (which he expresses dissatisfaction about). The problem is that the Max Rebo sequence is completely unessential and not just in the background like it should be.