The thing is, the amount of bonus content ALREADY OUT THERE (but technically "out of print") for the OT is huge. Hours of video of behind the scenes stuff, several deleted scenes, interviews, specials, gags, etc.
Empire of Dreams was cool for what it was (a 3.5 HOUR special mostly about the first movie and the phenomenon it spawned, with a much shorter covering of the two sequels) and perhaps longer than any of the specials on the prequel discs, but in terms of sheer volume... pick any of the prequels DVD's (AOTC had less than TPM, I forget how ROTS compared to the two), they blow the OT bonus disc away in terms of extras.
Yes, it helps that they made web docs and stuff of these prequels as they were making them. But it's not as if bonus content for the original trilogy doesn't exist.
What MIGHT be a reason why it didn't appear is because it isn't "Revised." It shows the painstaking hard work that went into the models, it mentions the old scenes before they were "special editionized." They show that Lucas did NOT plan "all along" to make several of the changes he claimed were always part of his original vision (some things, actually were closer to his original vision, such as the original Death Star battle, on story boards looks more like the special edition than the 1977 version, and the original view of the Sarlacc, or at least one of the concept sketches, looks more like the "Little Shop of Horrors" version from the special edition than what we saw in 1983). You also have embarrassing quotes from Lucas where he bad mouths the use of special effects to tell a story and stuff like that.
I know it sounds a bit like a conspiracy theory, but perhaps Lucas doesn't want to be reminded (and remind his fans) of how he and others viewed the movies as they were being made and when the first achieved success and fame.
But anyway, who knows. Sure, some people don't want to see grainy footage from the late 70's and early 80's with bad haircuts and people talking about how awesome it is to see models explode and puppets flail around. But a lot of fans DO want to see that, and want to have all their Star Wars content in one convenient digital archive.
Honestly, for extras, "Star Wars: Behind the Magic, CD-ROM" and "Star Wars: Making Magic" are much better in terms of overall bonus content than the Bonus SW DVD.