I think we go through stages.
Initially, I think many become addicted to the challenge, and knowing that it's all on you to improve, and that no political decision(Coach's son in your position) or lack of size, is going to keep you from reaching your potential.
For most, you have the potential to get out of it what you put into it. Or at least you are seduced into believing this to be true.
There's certainly one category you left out, especially for newer golfers, the self improvement one gets over time, and the Quixotic dream that your best golf is ahead of you, regardless of age.
I'm fortunate enough to play for many of the reasons Paul lists, but probably the main reason I became a life long golfer was the ambition to improve, AND, the enjoyment of the process as there is ALWAYS something you can do better, and there simply aren't enough hours in the day to work on all the elements of golf.
Over time that morphed to competition, then gambling(many bets-but prefer small units so no one gets hurt)and eventually evolved to seeking out cool places to play where it is the setting, course, playing companions and/or game that matter, not the status of the membership or status of the course(Lately, many/most of those places are often over run with status seekers and/or people I simply would not choose to play with when "not working")
As someone "in the business", there are certainly times where I practice or play when I'm quite tired and I'd prefer not to, but that, like any other job, goes with the territory.
As I get older, I still really enjoy teaching golf to people from all walks of life who have a desire to discover and learn, but generally my mind wanders to visiting even more remote regions of the UK, Ireland etc., so I think that's probably the way I'll wind my golf life down(Teaching a bit and travelling), if my body and finances allow.
I guess my point is we all go through stages, and play for many reasons during our life.
That and we don't know what else to do....