They're impossible to get into.
You either have to devote your life to the things or you get so completely outclassed by the people who do that you can't really enjoy yourself (playing and losing can still be fun, but when the skill-gap is so big that you don't even have a chance it's just boring).
Most serious fighting game fans are either unwilling or unable to teach new players, and the average skill level online has gotten so high that there isn't really any good learning environment available. Because skills often transfer from game to game, it's pretty hard to just pick up the new Street Fighter and go online because you'll be up against all the crazy-good people who have been playing since Street Fighter II hit the arcades and don't want anything to do with you. It takes so much work to be able to even begin having fun that it's just not worth the time investment.
I occasionally pick up a fighting game that catches my interest and spend a decent amount of time on it, but the experience has always been pretty negative except when I'm playing with a similarly inexperienced friend in the same room.
Et3rnalLegend64 said:
I know no one who's not already an enthusiast will listen, but every match is a chance to improve. It's just you and the other player, no distractions or excuses. Your style and knowledge of the game against his. Just because you've seen the character he uses doesn't mean you know how to deal with him. Your ability to react under pressure and adjust your strategies to each others' as the match goes on determines who wins. If the game was a simple "twitch fest" then any random person can win by mashing uppercut every time the opponent jumps. The genre has as much depth as you're willing to look for, which is why we who play find so much enjoyment in it.
Based on my experience, I think this is only the case if you already have an understanding of the system and the muscle memory to actually pull off combos (I don't mean just the really big ones, a lot of people just starting out can't do them at all) and there really isn't a good environment to learn those things. Listening to fighting game fans describe what they're doing in a match is like listening to a different language, even to someone who's invested more than forty hours into a given game. On top of that, the fighting game community is usually pretty unfriendly to knew players, and even in the rare event that someone tries to explain things to you they just come off as unintelligible and intimidating.
A lot of people say you just need to put some effort into it, but the amount of effort involved seems to be roughly equivalent to learning a new sport and I could learn a fourth language in less time than most serious players recommend people spend practicing just to get good enough to go online.