I still feel it necessary to bring this up every time someone says people "just stopped playing MK9 because NRS players can't play 2 games":
People did not just 'stop playing' MK9. MK9 had serious issues, at the engine level, netplay level, game logistics level and balance level. These were issues that were raised over and over, complained about for months, begged for patches for, etc. The game was not patched, the studio moved on, and the rest is history. Accordingly, many players who were fed up also moved on (even though at heart, we still have love for the concept of the game and the franchise).
This is the crucial fact that everyone seems to forget each month when this discussion comes up. It's not like people left a generally well-balanced, generally bug-free fighting game with solid netplay for another one. If things were different, circumstances might have been different, but a lot of people were just 'hanging in there' because they love the franchise and didn't have anything else they wanted to play.
If MKX is really solid, has good netplay, and is well-supported for longer than a year, it may become the first game to stick around through multiple franchise releases. But if it isn't, it's not accurate to just blame the players. Everyone should to be realistic.