Although this may not be the cause, Cam himself even said that there was an obvious decrease in skywars players ever since no projectiles was released. Obviously, this could have easily been due to countless other reasons, but I also think that no projectiles is a pretty reasonable reason that players left. I and a few friends all kind of distanced ourselves from skywars, simply because it wasn't the same. Those who had played skywars beforehand would either love no projectiles, or hate it a lot. There's no real in between from what I've seen. It's like a completely different gamemode, where your gear is all that matters. "Screw strategy and just bridge to the player! It's pretty much SG with some void in it!" is the message I was getting from no projectiles.
And the fact that most people always complained about people spamming snowballs and eggs made for a pretty good reason to remove no projectiles and replace it with a mode which doesn't include eggs or snowballs.
Again, Cam said that there's been an obvious decrease in skywars players since no projectiles was released, and what I said above kind of motivates the decrease. I and many others hated how it basically ruined the skywars we once loved. (The worst part was that it was almost always the outcome of voting, since you basically stand 0 chance of getting normal projectiles even if you vote)