Maybe he wanted to ride more than one race a year too.
j/k, but he said in an interview he wasn't happy with the role he was playing and Discovery's lack of effort to sweeten his contract. A friend of mine is a friend of Ventura's, and one day, I went over and talked to Ventura when I was hanging with my friend. Robbie told us that Landis just wanted a team where he would be able to lead, and he felt that he had more potential and would be happier with Phonak.
If you ride with Discovery, your focus is probably only on the Tour anyway- and if you want to ride several races, I get the feeling that would be frowned upon. I'm sure they want to train one guy "Lance style", but not everyone wants to live and die by that agenda.
Koffee