@yumi8228 Team Ninja chose the Sigma versions for the Master Collection because the original NGB/NGII code is scattered and unoptimized, making it cheaper to release versions the current team built rather than spending time and money recompiling legacy code they didn't create.
NetherRealm is now focusing on its next project and after more than two years of supporting Mortal Kombat 11, DLC for the game, including characters, has come to an end.