The compositing was so good in ROTJ that there were only a handful of shots that needed to be re-comped, I suppose. I think Lucasfilm also was feeling the strains of both time and money--ROTJ was in fact delayed a week and had the least amount of money put into it, but there are other factors at play there (it's usually claimed that its delay was because ANH and ESB were still doing strong business).

I wonder how "clean" the film actually looked with all the dozens of layers of composites, and the possibly-not-re-printed-wipes. The 2004 version got rid of all the grain and smoothed out the density fluxuations, and all the home video versions of the 1997 version are too soft to see that sort of detail. I only saw it once in 1997 so I don't remember how well it compared to the previous films in terms of that kind of picture detail.

Also, it was asked why the random re-comping? i.e. a sequence will start off original, then in the middle there is one or two re-comps, then back to original.

The answer is because they never really intended to do so much re-comping in the first place. But then ILMers would point out the odd shot that was noticeable worse than the rest around it, or that needed something smoothed out or moved. But the project was never supposed to be so in-depth or expensive, so they couldn't re-do every shot, nor did they want to, so they just picked and chose the ones they thought were the worst off. One side effect of this was that when the re-comped one shot and fixed it, suddenly it made another shot that didn't look bad before seem worse because everything around it was perfect, so they usually ended up re-doing two or three other shots in a sequence. In fact, ESB and ROTJ were never supposed to get the SE treatment, and the decision wasn't made until sometime in late 1995 or early 1996. This shows why so little work was done to those films, the 35mm negatives were in relatively good shape and the effects still held up pretty well and weren't in dire need of restoring and enhancing.