Bobby likes it on Tatooine, the peace and solitude he's not as young as he was, and there's plenty of younger bodies to do the hard parts. Case in point, the Winchester boys, though volunteering them for this Sith chase and that Imperial-base sabotage is only fair considering all the times he's their first and last resort. But it will never cross his mind to do anything but come running when they call: some of it is that he owes that much to their dead daddy, but most of it is that there are no debts between family, and Sam, Dean, and Bobby are all any of the three of them have left.