Geez TTL, you've limited the answers to the 3 worst reasons/ motivations for coitus. It's a chore to those who find themselves unhappy and unsatisfied in a relationship-- A hobby to those who have had no luck finding the right one-- A sport to megalomaniacs and undeveloped individuals-- A passion for people when it becomes an act of fulfillment and gratitude because of who the person is. (sorry I broke the rules and added a category)
I think for every individual it's different. For me, its a way of expressing physically what I feel in my heart for another person. Now , I'm fairly athletic so I suppose I could make that expression a sport, but sport is a competition with a winner and a loser and for sex to be done right, all the parties have to feel like winners! I suppose sex could be a hobby as well, particularly if one is prone to collecting. Collecting lovers, and perhaps keeping the event on film, might be one way to accomplish this. One thing sex is not, is a chore! Given a choice between having sex and say doing the dishes or washing the car, I think most people would have the sex, even if it was with just a collector!