The best guess is probably that it's several reasons. Obviously I think what you said is his main reason, but obviously there will be other minor things as well.
I only hope that it doesn't evolve into what happened with Pendulum, people asking SW all the time about PT while he's enjoying his solo-stuff, and he'll eventually go "this is my main thing now".
To be fair, I think GfD and Insurgentes are both equally awesome (if not better) to PT's best albums. So if he would disband PT and go for the solo-stuff (theoretically) I don't think I would mind that much. Sure, loosing PT would be sad, but I'd still be knowing that he would make awesome music.