I'd love to see one of those posters explain to me, rationally, how exactly they perceive it to be fun? Please try to explain yourself rationally (with broken English if necessary).
It's fun because there's a probability to make a profit. I mostly bet on esports matches, the thrill you get when watching the game you're betting on is what makes it fun. I gotta say betting makes watching the game twice as exciting. It's even more fun when you're winning and gain some profit, oh that feeling, it's satisfying.
You're correct it isn't as fun when you're losing, though. That's why I try to be as careful as possible before placing the bets to minimize the risk. Analyzing the teams, watching the news, etc those are part of the fun too.