Seeing as how "rushers" and "quickscopers" do NOT make up half the CoD population I think you're wrong. The population is dying because Ghosts is more about playing barbie with your character than actual gameplay. The competitive community also isn't to blame for the low population as it's a fairly small community as well. I believe the reason is that Ghosts has very little replay value.
This is where things might be slightly offensive to some. With that being said, if you're easily offended I suggest you read no further.
Without even going into gameplay dynamics Ghosts has no replay value. Most casuals good care less about actual game mechanics and just play to unlock all the goodies or for less awkward social interaction. What happens when you just hand a child anything and everything they want with no effort on their part? Well, that's what Ghosts did. Now that all the casuals have had every perk, every weapon, every attachment, and every "operation" just handed to them they have lost interest with the game because nothing actually has a value in Ghosts. When you just hand someone something that they deemed valuable for nothing it looses value.
CoD has always focused heavily on player investment and Ghosts broke the standard model. Why would someone that doesn't care about gameplay mechanics continue playing if they had no incentive to do so? Well as you can see with Ghosts, they won't.
