Serious fighting game players, people who play to compete, generally don't consider a story mode as necessary or important, even if it is something they would enjoy, because to them it's a side dish.
But story mode
matters if you want people outside that specific audience to pick up your game. I refuse to use the term "casuals" because many of the people in this broader audience play shitloads of videogames, but regardless of what you call them there's a very large chunk of sales that can come from the general gaming audience. Look at how well Netherrealm's fighters sell, look at the mindshare that exists outside of the FGC. People absolutely buy those games for the story mode, then either trade them in or keep them around to play matches with buddies from time to time.
This shouldn't even be an argument anymore. Having a story mode does not preclude having good gameplay mechanics, it doesn't take away from the things that makes a fighting game great for tournament play. It
does, however, draw in more people to buy the game for short term engagement, and more sales is a good thing for ensuring your favorite fighting franchise stays afloat.
A game isn't necessarily bad for not having a story mode, but having meaningful single player content will generally earn you a lot of good word of mouth, good press, and sales.
I think the "casuals" people are talking about won't stick around no matter what. MKX does a lot to get that audience but I imagine most of them bail out after a few weeks too.
I think there's a big difference between the hardcore fighting gamers who keep your game alive long term and the general gaming audience who are looking more for short term engagement. Good single player content, especially a good story mode, helps bring them and their money in, and even if they don't stick around the game made money off of them. And if they were pleased with that experience, they'll pass along positive word of mouth, leading to more sales from gamers looking for that short term engagement and maybe something to keep on the shelf for when buddies are over.
You definitely appeal to these two crowds in very different ways, but because a story mode does not impede the development of a healthy core fighting system the two should not be seen as opposed in any way. And there's nothing WRONG with people paying to play a fighter for a while and leaving it, especially if they were never going to be the type of person to stick around anyway. It definitely takes a certain type to put time into a fighting game. As mentioned above, fighters aren't team shooters, these things break you when you first play someone with real skill.
