> Me and a friend were just chatting how annoying it is monitors stalled out at 4K. I think I got my first set of 4k monitors ~15 years ago (!) and there's been no improvements since then apart from high end pro monitors resolution wise.
Multiple reasons.
The first one being yield - yes you can get 8K screens, but the larger they get, the more difficult it is to cut a panel with an acceptably low rate of dead/stuck pixels out of a giant piece of glass. Dead pixels are one thing and bad enough, but stuck-bright pixels ruin the entire panel because they will be noticeable in any dark-ish movie or game scene. That makes them really darn expensive.
The second reason is the processing power required to render the video signal to the screen, aka display controllers. Even if you "just" take regular 8 bit RGB - each frame takes up 33 million pixels, so 796.262.400 bits. Per frame. Per second? Even at just 30 FPS, you're talking about 23.887.872.000 bits per second - 23 gigabits/s. It takes an awful, awful lot of processing power just to shuffle that data from the link SerDes around to all the control lines and to make sure they all switch their individual pixels at the very same time.
The third is transferring all the data. Even if you use compression and sub-sampling, you still need to compress and sub-sample the framebuffer on the GPU side, transfer up to 48 GBit/s (HDMI 2.3) or 77 GBit/s (DP 2.1) of data, and then uncompress it on the display side. If it's HDCP-encrypted, you need to account for that as well - encrypting and decrypting at such line speeds used to be unthinkable even two decades ago. The fact that the physical transfer layer is capable of delivering such data rates over many meters of copper cable of varying quality is nothing short of amazing anyway.
And the fourth is generating all the data. You need absurdly high definition textures, which requires lots of VRAM, lots of regular RAM, lots of disk I/O, lots of disk storage (your average AAA game is well beyond 100GB of data at-rest for a reason!), and then render power to actually render the scene. 8K has 16x (!) the pixels of regular FullHD (1080p).
What's stopping further progress? Other than yield and simple physics (similar to microchips, the finer the structures get the more difficult and expensive it is to make them), the most pressing issue is human visual acuity - even a human with very good vision can only make useful sense of about 74 of the theoretical 576 megapixels [1]. As we already established, 8K is at 33-ish megapixels, so the usual quadratic increase would already be far too detailed for 99.999% of humans to perceive.
Yes, you could go for intermediate sizes. 5K, 6K, weird aspect ratios, whatever - but as soon as you go there, you'll run into issues with video content because it can't be up- or downscaled to such intermediates without a perceptible loss in quality and, again, a lot of processing power.
[1] https://clarkvision.com/articles/eye-resolution.html