Re: philosophical or practical martial art?
Anything you do for the right reasons is fun. So fun is related to proper training. It's a result rather than a purpose.
With correct purpose you have fun.
On the other side of the coin if you are doing something for the 'wrong' reasons then for you it's harder, heavier going and not so much fun.
This applies to everything no? Remember being stuck in a classroom studying a subject you neither wanted to do or could see any use for in your life? Not much fun eh?
In fact I would say fun is a basic desire rather than a purpose.