This probably has been discussed before, but the subject came up when I was talking with a guy at work the other day.  He is also an official, albeit not basketball (football and baseball).
He said it fulfills a need to continue to be involved with the sports he played as a kid but is too old to play now.  He said the alternative would be to coach, but he "would need to get a lobotomy" to be able to handle that.  
 
I told him I work basketball for three reasons.  First, it gives me some exercise.  Second, I just love the game and really like to see kids progress up the ladder over the years.  Third, (and I am not kidding here, ask my psychiatrist) I enjoy being in a position of total authority.  Maybe because it's a counterbalance to my home life.  
 
Any other reasons you guys do this?