Actually one of the pinned Reddit posts is :"No, it's not dead, stop asking."
Is it booming on PC? No. I wouldn't claim that. It has certainly lost population since the heyday of launch, but dead it is not. If you want a dead game see Wild West Online on Steam charts or poor Battleborn which never hit its stride and is floundering. Only Turf Takeover is consistently populated or the portal events, and a lot of names you see will be consistent, with a few new ones here and there, but dead it is not. It can be frustrating if you like the co-op ops modes as you can run some with no takers on an public run but then get a full team that hangs around for a bit the next day.
If you want non-TT modes you have to play bot matches mostly.
The new DLC coming soon should help revitalize it some. It's not perfect but still a solid game.
Edit; In fact it's the very first thing in the FaQ:
https://www.reddit.com/r/PvZGardenWarfare/comments/9fyria/frequently_asked_questions/
Later down it does state:
"
Q: What About The Player Count?
A: The playerbase is healthy on both PS4 and Xbox, but PC has a much lower playercount."
Lower but still present. I play a little pretty much everyday, some days more than others of course, I'm also playing a lot of Paladins lately.