I'm not so sure MK1's woes speak volumes about anything else besides MK1. Has any NRS game ever had three years of content updates?

I remember when Riot first bought Radiant Entertainment, all the discourse about how the League fighter would kill every other FGC title just by being F2P and having Riot money behind it.

Then they took a whole decade to release, and the development hell was not kind to the final product. But I'd also just say that the landscape changed so much in that decade, other fighting games have become a lot more mainstream now, enough so that this was not enough to compete with them anymore.

But doesn’t it speak volumes about the genre of the eighth best selling game of 2023 can’t support three years of service (as in meaningful content updates)?

Oh, they could have, but this is NetherRealm Studios. This is the first time they went 4 years between fighting games. Ordinarily, they're on a two-year cadence, and each game sells multiple millions of copies. Which do you think makes more money? Selling a game at $60-$70, or selling DLC to people who already bought an old game? The experiment they tried this past game was the big cinematic expansion, because it was successful for MK11, but they were going to do a series of episodes for MK1 that basically meant the story was never-ending; and they replaced the Krypt mode with Invasions, which was also intended to be never-ending. Neither of those things took off, and this big cinematic expansion also cost $50. Their average customer was not thrilled about Kameos, so it makes far more sense for them to just put out the next Injustice game, as long as their parent company can keep from collapsing long enough that DC superheroes are still intellectual property that this studio is allowed to use.

While there weren’t any Fatal Fury entries, the characters did have presence over the years via King of Fighters, and Mai and Terry were even in SF6.

King of Fighters games are not multimillion sellers. People being vaguely aware of Mai and Terry does a bit of help, but brand recognition takes longer than that. Fatal Fury didn't get enough production value out of its development budget to do anything like SF6's world tour mode, or NRS's story modes, that would bring in the less sweaty players. Instead, it just got Saudi money thrown into marketing a game that was never going to make that money back.

SF6, arguably the biggest game in the genre, is currently in 60th place in the steam 24 hour charts. You might argue consoles have a higher share for the genre than games you find on steam, but still, that’s not totally mainstream.

No, in fact, that's an old way of thinking. Since the pandemic, there have been a few ways where we've been able to measure the share of players on each platform in certain fighting games, and PC is the biggest one every time; I'm sure there are outliers, but PC is the largest platform whether we're talking about fighting games or not. 60th place on Steam's charts is phenomenal and not at all niche! There are so many games on Steam being played by about 140M people per month. Only being beaten by 59 of them is incredibly successful.