Well I would have 3 reasons. Three big reasons
- Usually they take enourmous amounts of time invested, in order for the player to get half decent. For example in dota/lol you need to learn tons of mechanics, interactions, spells heroes etc just to be able not to suck
- Even if you do learn, getting better is another story. After you've learned you need to invest double the time to actually be good.
- Playing solo, and this is linked with the community. If you don't have a stack of 4 friends that play then good luck.
As far as I can say, most of the time I didn't even have fun playing, because I was too stressed out in order to do something. Hell rather than playing these types of games I would gladly play something like WoW or a single player game where I can actually have fun and be engaged.
What I have to give them though is the fact that the esports scene is indeed very well established. I have discovered that spectating tournaments is more relaxing and engaging than playing, haha.