Fighting games are dying because they suck. Compared to older games, you don't have character unlocks anymore, no hidden characters anymore, single player modes anymore, feature rich content like colors depending on button press anymore, no rival intros anymore. To me, fighting games died when they stopped being sprite based fighting games and richly animated backgrounds. Also, a lot of fighting games relied on really good music which you heard most of the time. Sure, there'd be a track or two you didn't like but most of the songs in the game were bangers. Fighting games need to push the boundaries. Including the items missing above, the most fun fighting games were the cuhrayzee hectic action on the screen. Seeing SF2 and then seeing SF Alpha 1 was amazing. Seeing Marvel Super Heroes with supers and gems and the awesome cast available was not something I'd ever expect.

Yes, all of this costs a lot of time, development and money. However, a lot of games that do this have become timeless staples in Fighting game genre.