I have no insider knowledge, but I'll take a stab (assuming that the money was equal):
Eugene is nice. The weather is better than in Austin, although it still gets hot. Visiting in the summer and then coming back to hot AF Dallas may have given him pause.
Far from family and high school friends. Some people like to go do their own thing. Plus maybe he wants to have fun in college - like fun fun - and doesn't think he can do that in Austin where he's so close to family / friends. Fewer people to report back to mom if you show your ass on Saturday night.
Rashaad Samples / Lanning's staff are good recruiters. I'm sure they had a good pitch. I don't know a ton about Junior Adams, but having the WR be an OC suggests that WR will feature in the offense.
Their WR room has plenty of talent, but isn't nearly as stacked as we are at the position. It's pretty much Evan Stewart and Tez Johnson. The others are contributors and one or two might even play on Sunday, but there are fewer people between Moore and the field at Oregon.
I doubt the QB room had anything to do with this. I would think that factor favors Texas. But maybe he hit it off with Dante Moore in a way he didn't with Manning? I don't know.
If he's not happy at Oregon he can always leave. Texas will welcome him with open arms and no one in his family will question the decision. He would probably catch a lot more shit at home if he tried to do the reverse.
Him calling Evan Stewart a role model or whatever tells me that his judgment may be somewhat suspect, or at least that he's not using the normal metrics in making his decision. Stewart went to A&M for money and to be the feature WR. I don't think he cared that much about the larger university experience or the team's success. I don't fault Stewart for being merc, but I do fault him for being a duplicitous, lazy little shit. Maybe he got in Moore's ear and told him that all coaches are liars and that Moore needs to look out for No. 1 rather than listen to any coach's pitch. That would make sense if the bulk of your experience with coaches is Jimbo. Lanning probably seems like a Saint in contrast.
Speaking of Evan Stewart, weed like legal in Oregon. It is not in Texas. One fewer thing to worry about on Saturday night.
I'm sure that money had a lot to do with it, but based on what people have said on this board I'm assuming that we were happy to equal whatever Oregon was offering. So the things I've listed above seem to be the difference makers.
Edit: And they do have snazzy uniforms. Not my style personally, but I'm a 40-year-old white dude.