Gaming on 4k (native) is still a minority.
It's popular in hardcore circles like this forum, it's not popular in the casual market.
I **** you not, when I talk to my casual gamer friends - they don't even know what resolution is, when I tried to explain what 4k resolution they look bewildered, they don't know their current monitor is 1080p.
These types of gamers are gaming on 23 inch 1080p screens and they bought the cheapest model possible - if the cheapest model was a 720p screen they'd have bought that instead without realizing. For them it's all about the games themselves, not the graphics.
4k will only become popular when they stop making 1080p AND you can get 4k screens for $150usd - and it's not because the casual market wants it and is waiting for it, they buy these screens by accident and they will only upgrade to 4k when 1080p is no longer the cheapest monitor to buy.
It's EXACTLY the same thing that happened in the TV market - 4k only became popular when they stopped selling 1080p. If they still made 1080p TVs on mass and they were cheap, 90% of the market would be buying 1080p today still.