1) Pride/Greed - George basically went downhill. He either wanted to milk his cash cow and so re-marketed his old stuff, or just lost touch and wouldn't listen to input, advice, or view his works critically, thinking he was untouchable. These seem to be the most common views.
2) Well meaning, but lost his genius: as a music writer, I'm familiar with this phenomenon. Sometimes you write part of a song, and it just WORKS. It flows, it's great, you have a vision. But trying to complete it, suddenly it just doesn't work anymore. Perhaps he really is trying, and for some reason what flowed and jibed before just isn't coming anymore. This seems to be at odds with what he says in interviews about the quality of his work, but maybe he just wants to put the best face on it.
3) Utter genius: I find this theory the most interesting. ANH was different from eps 5 and 6. The script was a little simpler, the plot was a little more fairy tale-ish, the whole thing was more campy, lower budget, and so forth. In the CONTEXT of 5 and 6, though, 4 becomes a real masterpiece. Not just enjoyable and great, but truly respectable in other ways. In a similar way, I at least enjoyed TPM much more in the context of AOTC, it gave it context and substance and purpose. Perhaps episode 3 and these changes to the OT are all part of a master plan that needs to be completed before it makes sense. Perhaps the SE releases and changes were all part of this larger plan that we can't appreciate until it is done and can see the whole thing.
I held onto that hope for a long time, but it is waning. I don't see how certain changes can fit into a whole, but I haven't seen the projected 2007 version of all 6 films yet.
Anyone holding out hope? Any idea what caused this change in what used to be a beloved man to all of us?