Treyarch has announced that the MP5 had been nerfed in order to alleviate weapon balancing concerns in Call of Duty: Black Ops Cold War.
The SMG was arguably the strongest weapon in Multiplayer, and was effective in almost every single in-game scenario.
The developer is always wanting feedback regarding various elements of the game including weapon balancing and the current state of the game.
This is the first weapon update to drop on Black Ops Cold War. Another weapon update is expected on December 10th, coinciding with the launch of the first season of post-launch content.