How come there are still no 4K 60fps KVM devices?
Software solutions like Moonlight/Sunshine have been able to do that with near-zero latency for a long time and they are not even the first. Phones have chips capable of capturing 4K 120fps. Why is it so hard for KVM devices?
Because no one manufactures a cheap silicon chip that converts DP Alt-Mode to UVC at 4K. There exist great <$5 ultra-commoditized options for 1080p HDMI -> UVC but as soon as you move up to capture 4K it gets super expensive for the silicon alone and the engineering complexity goes way up as well.
Generally all these devices are just slapping together a few existing silicon chips. If the chip they need doesn’t exist, no ones really going out of their way to overengineer a different solution for which price to consumer would be prohibitive.