DeathscytheX

I blame their game engine and design concept. it's the same game over and over again except now with perks that emulate lag switching (FTL jump) so cheaters can blend in more so they get less complaints.

You're partly right. They've let the game get stale with a complete lacking of new ideas. It's either the same old thing, or another game's idea. They've forgotten how to make outstanding maps and decent gun balance. Instead they've recycled, mixed, matched, and divided up their perk systems into a overly complex mess more jacked up than the US tax codes. Perks use to deliver balance while complementing your style of play. Now it's just a way to close the gap between noobs and decent to good players. 

When you get killed because of some bullshit that required no skill, and there was very little you could do to counter it, that isn't fun. It all started with death streaks, and now it's just sewn into the perks. What they've done is gotten rid of the middle class of COD. players like me that were really good at the game, but not pro level good. Now COD is filled with shit players and God like players with no middle ground.  If you jump in you're either going to be on a team that rekts or you're going to be rekted.

They abandoned their core audience to long and where trying to reach a base they had no business catering to. Now with Overwatch, Titanfall, Halo, R6S, BF, and Gears of War saturating the market, those players that made COD what it was have moved on to something else. There is a lot more competition than 10 years ago. 

I bet Overwatch took a large chunk of their player base with it's competitive mode.