The fighting game community can only support 3 games at a time: the newest Street Fighter game, the newest Marvel game, and whatever else is the most recent big-name fighter. This has always been the case, and that’s just the way it is. For ever and ever. Amen.
Most people claim that the game was too tough to play. Considering KOF’s combo system was based around cancels while SF4’s is based on extremely tight links and Marvel’s is constantly working against you with the hit stun decay system, it clearly wasn’t the execution that was holding people back. It was likely the fact that KOF is more of an old school fundamentals style fighter and this generation of players wouldn’t know a footsie if it kicked them in the head. Fighting games aren’t made with fighters in mind these days, they’re made with training mode monsters in mind.
Another common problem people sighted was the netcode, and while I will give you that the netcode was hot garbage, 1) people still play Marvel and SF4 and god knows they are unplayable online, and 2) Steam Edition’s online is among the best netcode I’ve experienced outside of GGPO and it’s a god damn ghost town.
Just remember - dead games are the only games worth playing. It’s been that way for at least a decade.