How many people use their pc for a single use, if most don't why are screens aimed at single use scenarios.
Fact is people swarmed all over 120hz 1080p screens when they finally became available so they pushed, and made 144hz screens, people got them, then they finally made faster slightly higher res screens, and people bought them. The demand is there, the manufacturers are just stupid.
I both use the desktop and want more screen space and resolution to fit in say netbeans, a pdf and webpage all without having to app switch constantly. But I also game, and maybe I won't have the best graphics cards.
Put it this way, I have a 1080p 120hz screen now(well a few of them), so if I bought a 4k 120hz screen, primarily for the desktop advantage, and then I had a 1080p image upscaled to 4k, I wouldn't have a worse image, maybe no better, but I'm still better off for the majority of my screen usage. If I actually have the graphics cards then I have an advantage.
120hz is smoother in windows, on the desktop, 120hz is smoother in games regardless of if your fps is 5fps or 500fps. higher refresh rate means less screen blur for one thing which is a massive difference. 1080p 120 vs 60hz is night and day for most people. Everything feels smoother and better, less blurry. Scrolling on a webpage is smoother and less blurry. 60hz is just rubbish, it's a standard that should utterly die. It sucked on CRT's badly, and it sucks on LCD, for different reasons, CRT it was flickering and on LCD it's screen blur.
Every time they make a higher res screen with a decent refresh rate it sells by the bucket load, I can't believe they aren't pushing it.