I just finished 12 weeks with the Fireflies and there was something interesting data regarding the statistics. So it turns out that as of right now 554k people have played the multiplayer. This is only half of the users that purchased the game. The MP, especially in the Remastered version because of the expansions, is a big part of the Last of US and is enjoyed by most of people who have played it.
The game is obviously singleplayer focused and may therefore many people haven't really felt the need to try the MP out. There is however a dedicated fanbase and there are a lot of people playing it very seriously which can be concluded out of the other open statistics. There are 78k people that reached a clan with over 88 people which is difficult to reach and you need to play quite a lot to get there (my highest so far).
Stories unfolded with my home made rap songs. Feel free to listen here with lyrics: https://youtu.be/vyT9PbK5_T0