It's because the game doesn't really feel like CoD besides how the gun handles. The exo movements break the flow of the game that CoD players are used to and allows players to cross lanes with little trouble making it tough to play in the traditional defensive manner. You pretty much have to rush in this game unless you have a party of coordinated players that can lock and funnel the flow of an otherwise chaotic game.
Edit: I expected this reason. Introducing a new type of playstyle will indeed break that "formula" and doesn't necessarily help fix or replace it.
As a rusher myself I don't hate the game but I probably get 50% enjoyment and 50% frustration and is very tiring with having to keep focused on enemies jumping around constantly flying through the air. SBMM forces players to connect that otherwise wouldn't have, so you'll be connecting with others many states away and the netcode just can't keep up with the speed at which the better players play this game.
Edit: Now this I never expected and perhaps different teams testing this didn't bother to consider the how difficult and broken the netcode would be. Also, the MP team should've consider the amount of distance, speed, and refresh rate in your ability to thrust would be too much a dynamic for player as a majority to handle especially when you implement a jetpack/vertical thrust into your game when pros know how to abuse a feature.