Besides which, he is from the generation that knew how too much of a good thing was really really bad for a person. We're spoilt. We get too much of what we want. we demand so much much from Lucas when he doesn't have to give us anything at all. It could all sit in his private museum to amuse him privately...
I'd love to see every moment of footage ever shot but it isn't going to happen. Lucasfilm, because it's a corporation not a man these days that makes the decisions, will no doubt spin out re-issues of these DVD disks ad infinitum so long as the money rolls in and the fans still buy them. It's not insidious to use such a practise it's business. Supply and demand. Don't put all your eggs in one basket and save a little of the good stuff for later. Perhaps this third disk will contain the rest of the lightsaber battles in the generator complex. I've heard that Lucas culled a lot of that footage so he could release it later and make money from fans willing to shell out for 'lost' footage. Seems about right to me. Why not? The trouble with being rich is that so little wealth is actual physical money. Most often it's just on paper like a random figure someone made up. Without physical money in your hands the temptation is to just keep doing what you always did and work at making money from whatever it is you do.
But most likely is the theory that they didn't think it would sell because so many diss EP1. It must have been a mighty shock to see the DVD hit the high notes in the returns figures. So obviously the guys who market this stuff will be anxious to capitalise on the success of the first releasre by chucking out more of the same.
Personally I'll buy the third disk if it comes out. Partly out of curiosity and partly to complete the disk set. Partly cuz I'm a mug and partly cuz I like the behind the scenes stuff just as much as the movies. I just hope they do the same with the OT DVD set -Three disks each with all the extra toppings you can eat would be just peachy.