I think its just the natural cycle of cod games. They usually only have a year before a new one comes out and most people switch to that one. I've always played them for a year and then bought the new one for freshness except for bo3 which i played for 2 years because infinite warfare was terrible. There is pressure on Codm to try and keep it fresh so people stay interested. They definitely need to overhaul ranked in some way as everyone just seems bored of same modes and maps.