I believe it was the low character count. Fighting games depend on gameplay, roster and balancing. Right now, KI don't get points for the second and the last one is subject to changes when more character are introduced.
Despite that, it needs marketing. It was a bigger franchise in SNES/N64 era, but it's just to much time out of scene. Younger games probably don't even now it is a sequence to a series of games.










