The Lincoln Riley move is an interesting one. There seem to be some rumors that he wasn't happy about the move to the SEC. Surely makes more money for the athletic department, but also makes his job a lot harder.
IMO there is also something to be said about the quality of life in LA vs Norman. Not just in terms of a "higher-class" society, but more in how he is able to live his life. I'd imagine he can't really go anywhere in Norman without being recognized. Can't run to Target, can't go out to dinner unless he's getting a private room in the back, can't go to school events for his kids, etc. In LA he'll be a C-list celebrity, and will be able to do those things in relative anonymity. Some coaches probably love being the king of a college town, but others don't want the extra attention when they are off the clock, especially with a young family.
I don't get the sense this was a money thing. He's probably not getting a huge raise in the net with the higher taxes in California. Was making about $8M per year at Oklahoma, and I bet he could have gotten them to match whatever he was offered by USC if he really wanted to stay.