I really don’t want to just link you to the Dom 101 article that addresses exactly this, but basically, when a game gets competitive, and there are two players working on an even level to one-up each other, each using every tool at their disposal to outplay the other, those two players are most likely having more fun than any kids sitting around laughing at how much “fun” the crazy, flashy, ultras are.
Competition breeds a more rewarding and satisfying kind of fun. If I’m playing “just for fun,” I might enjoy mashing buttons and seeing some neat combos and flashy moves, but once the round is over, the experience is gone. When I play a hard-fought, incredibly tense battle where one mistake could mean a loss with people watching, and elimination from a tournament, and I scrape by with a clever trick or well-placed combo, and win the match, that feeling will sometimes stay with me for hours.
Any time you really achieve something you decide that you want, you’ll find that you get a lot more enjoyment than when your goal is simply to “have fun”