Initially, the multiplayer game of The Last of Us was born as a game mode for The Last of Us II, but the ambition grew and it became an independent title. Naughty Dog has been working on this project at least for 4 years.
Some days ago, the company issued and announcement on Twitter confirming that the game needs more time. Jason Schreier has more information about the process; according to the journalist, the development of the title has slowed down and the team that worked on it has been reduced after a recent evaluation. A small group remains in the project and part of the previous workforce has been moved to other games.
Apparently, Bungie evaluated the game and concluded that the multiplayer project could not keep the players for a long period of time. This evaluation led to the revaluation of the game.
So, we will have to wait to see something.