You are making a generalization. In any competitive game I play, the majority of my playtime is taken up by ranked gamemodes. While I like to rank up in these games, it's not really about the rank. It's about knowing that everyone else there in that lobby is there to win. People take the game seriously and that's what makes it enjoyable. When you take the game seriously, it's a challenge. You actually have to think about how you can win and work with your teammates to reach that goal. Some people are really good and it's humbling to see them play. Others are really bad and it's funny to watch them. It's a fun and unfortunately addicting experience other kinds of games have difficulty replicating.
If in a competitive game, you get dogged on non-stop, it's time to find another game or play the casual mode until you improve. I don't play CS:GO anymore, but when I did, I didn't touch competitive until I had 100 hours on the game. This is because I knew that going into ranked as a complete newbie would be hard. If you don't have the time to dedicate to succeed in a ranked game, just stick to casual gaming. There's nothing wrong with that, I like to play party games with my friends all the time.
tldr: it's fun because challenging or something yea
