I use a 4K 27" screen at a distance where it uses the same scaling as a 1440p 14" laptop. Looks great to me, but if your vision is better or you're using it closer then it may not be enough. Other people use 4K TVs or 65" screens to be able to set them farther and keep their vision more rested for the same angular resolution. Resolution requirements depend massively on how you setup your workspace and the quality of your vision. There are plenty of people that use software scaling for 1080p 14" laptop screens as they consider normal sizes too small for example. The range of configurations is very high and you're on one extreme of that range. There's nothing wrong with that but that's probably why you're frustrated with the lack of options on the market. For most people even 4K 27" is already overkill and 1080p external screens sell well instead.
Please answer the question I posted. "Do you really believe that people use these 4k@27'' displays at a different distance than mac users use their 27 inch iMac?"
Yes. I do believe an external 4k 27" on a laptop is used differently than a single screen on an iMac. I also believe people use iMacs in ways that are different than what you use, which was the whole point of my answer. People use screens in all sorts of different ways. Most of them have resolution requirements much below yours, which is why the market apparently doesn't cater for your needs.
For most people not using macos 4k is overkill and 1080p can be enough not by itself but because the other two major OS (windows and linux) have antialiased text with subpixel hinting. I.e. they can exploit the pixel internal structure to display sharp text even on low resolution monitors. Apple deliberately decided to ditch their own implementation as you don't need it for retina displays and they only sell and care about retina displays.
