Everybody knows the bulk of fun in fighting games comes from battling against other players, not AI combatants that are either brain dead or frustratingly cheap. Unless you have a group of friends you really enjoy gaming with, you're going to get most of your PvP combat online. Where outside of playing during the launch window, or being an established fighting game player, you'll likely have your ass pounded into the dirt repeatedly by much better players, with a near 0% chance of victory, and a W-L record verifying my claim.
It just screams fun.
Every gamer worth his or her salt recognizes Ryu or Chun-Li, but when's the last time they played with them? Outside of the fighting game community (FGC hereafter), the odds are good it was Street Fighter 2 Super Ultra Turbo Chaos Emerald Championship Edition on SNES, or maybe Ryu in Smash. Why? The barrier to entry for fighting games is too damn high.
For a few reasons, new players can't enjoy the fun part of the game right out of the box. Let's ignore sticks, which require a significant investment of money and learning a new control method, and assume we're just going to use a standard game pad, like most newbies do. Having done so, we can see the first major road blocks for beginners are inputs.
Having to quickly perform a series of directional inputs, that can range in complexity from the quarter circle forward, to the Z motion of the famous Shoryuken, and even full 360 inputs, adds a fairly unique physical component to execution in fighting games. As a beginner some of these are hard to consistently pull off when just standing there, let alone in combat where you have to plan your moves and make changes on the fly. Performing under duress is something even the professional players can flub.
Before a new player can be competitive, they have to spend a large amount of time just practicing how to do the moves. This is accurate to real martial arts, which I admit is kind of cool, but your average gamer doesn't want to spend varying amounts of time ingraining motions into their muscle memory before they can actually play “the real game.” That's not even enough, though, because then they have to learn how to properly use the moves they've mastered. That's the next major road block: Roster sizes.
When new players finally get equipped with their tools, they only have half the information they need to be competitive. The other half, knowing when and how to use their tools, is based on knowing your opponent's moves and how they work. So now the new player has to learn match ups between characters. The number of characters on a roster varies, but Ultra Street Fighter IV ended up having over 40 characters. Even if newbies concern themselves with only learning the popular ones, that's a metric crap ton of information to process.