It's also because Spielberg is wise enough to leave classic films alone (or at least offer a choice of versions in the case of ET), and Lowry had a LOT more time to clean up the Indy films, whereas they were only given 30 days for each SW film, I believe. The only explanation I can offer for the awful job done is one of these:
1. Fox views this dvd set as just a temporary holdover until the 2007 release, and so little effort was put into the remastering. Most of the reason the films were put out was because of demand, not because GL wanted them out yet.
2. GL made numerous errors intentionally to build a potboiler of demand for the true versions, and so consumers end up double or triple dipping for the same films-in other words, it's part of a much larger marketing scheme.