Well some people get triggered at the thought of SF & Tekken in general, but props to Shimbori for showing respect to the competition. In terms of casual players, MK & Injustice attract a shitton more than any other fighting game. Easily has the most disproportionate ratio of casual to competitive players.
Free Step Dodge
Force_of_Nature
deathofaninja
So the King of Fighting games is determined by how many players play it? I guess that makes sense. Although it really only has to do with marketing... not about how fun the games are. Fortnite is popular, but it sucks balls. So does Tekken 7 and Street Fighter V. They are both boring games with characters I can barely look at without vomiting on myself. Those games are the king of corporate dick and that's about it.
ChaolanLegacy
SF being a king of fighting games is a no brainer. It is one of the two games(famous ones that is) that is probably the oldest out of all of them and it defined 2D fighting games as a whole. Tekken on the other hand is "the best 3D fighting game of all time" because of Tekken 3, that game was what put Tekken and probably 3D fighting games on the map too.
deathofaninja
It's such a popular game they market ads on the characters. 
And give you advertisements and all that other corporate shit that can bite me.
And give you advertisements and all that other corporate shit that can bite me.