A lot of air force bases or military bases in general have golf courses. Presidents spend a lot of time while traveling on military bases, so many of them tend to pass the time paying golf.. You don't really think they should be working 24/7 now do you? Everyone needs a break from time to time just look at all the time off Congress has...
George Bush jr played a hell of a lot of golf as well..
So did Bill Clinton (just not as much)
as did many others before them...
It's a outside activity they can do and on military bases it's relatively easy to secure for the secret service so it's a favorite past time of many former and even the current president.