He wasn't asked to play in last years ram slam so signed a multi year deal with Melbourne for the big bash.
This year they did want him for the ram slam but it was always gonna be she or as big bash starts next month.
Does he only care about t20? I don't think he does. But he knows his body is on the Devine and ha knee issues, when he was told he had a chance with England he played 4 day cricket, as soon as he was again told he didn't have a chance.
He took himself back to the format that both pays the most and does not effect his body as much.
At mid 30s your not gonna travel the world playing the 4 day game knowing you have no chance of ever playing a test again.