CoD and LoL have a lot of other things in their base outside of the actual gameplay going for 'em, as well.
First and foremost, I think the social aspect of both games (in a cooperative sense) is a tremendous draw that also keeps them hooked. You can't really queue together with your friends in a fighter.
Their emphasis on online play is convenient for many players and they've provided strong structure for ranked/league play, which is attractive to players who want to assert their skill.
There're plenty of carrots-on-sticks to keep players playing, as well. More weapons, more perks, more prestiges. More champions and runes, rewards for doing well in each season.
For LoL in particular the Free-to-Play, Pay-to-Not-Grind model is tremendous in creating a large playerbase.
Most of these things are extremely attractive to just about any audience that isn't Japan, which naturally results in a largely Japanese developed genre like fighting games to be built around completely different philosophies. In accordance with this line of thought, NRS as the sole major western dev in fighting games attempting to bring some similar ideas to their games. King of the Hill and the large lobbies are a valiant (but not entirely successful) attempt at creating a strong social atmosphere in the online play. The XP system in Injustice mentioned hither and thither seems to have obvious parallels to the carrot-on-a-stick systems I mentioned above.
Superior netcode, a more in-depth online competitive structure, and incentives to participate in that structure would be key additions to pushing a fighting game into the kind of limelight we see other games in (and I don't think these things necessarily need to come at the expense of local communities/competition, despite what some may think).
But this is just like, my opinion man. All of this.
