This is a trade-off with frame rates and rendering quality. When having to choose, most gamers prefer higher frame rate and rendering quality. With 4K, that becomes very expensive, if not impossible. 4K is 2.25 times the pixels of 1440p, which for example means you can get double the frame rate with 1440p using the same processing power and bandwidth.

In other words, the current tech just isn’t quite there yet, or not cheap enough.