just a natural life cycle : a good game comes, people analyze it , dedicate to it, enjoy it, and so, until it becomes boring and repetitive, and naturally , we move on and go for the next one ..... happened with MK9, it's happening with IGAU, and will happen with KI3 and even MKX, when the right time comes ..... nothing last forever
there is no necessity for drama regarding this ..... normally, for NRS games, if you go for a simple observation you can see that the first year after the official release (when the game came out), it's the more enjoyable one for that specific fighting game : the period where everyone are excited with the new game, and discuss and take participation in every single topic and question regarding that game .... in the 2nd year, people already have experience and improved skill in that game, and so, still the game life cycle is good .... so in the 3rd year, probably the developer team announces a new game, and so, we can see that normally, is a better or improved version regarding graphics and gameplay mechanic than the last one, so, we go for that thing, to test that game .....
it's a natural human desire trait to go for the next stuff, if it's better and more interesting than the previous one.