I'm guessing he is tied in with various sponsors contracts so can only go when they are finished or else have to refund large amounts of money.
Then again maybe he just loves to get up there and play and as someone stated in the thread if he is still earning half a million a year then that's an incentive to hang around.
Possibly a question of what does he do next. As it appears that a career in the commentary box is off the cards then his options are possibly limited to sitting in the pub and the odd sporting diners as guest speaker. If that is the case then I would be tempted to hang around on the pro circuit for as long as my ranking allowed me.