Supporting 4K to a limited list of known hardware like AppleTV 4K, Roku, etc is much easier than trying to imagine the endless possibilities of what ever frankenputer you've assembled running whatever distro you've chosen while using whatever excuse of a driver you've managed to install for your hardware. Now mutltiply that across the larger number of windows users.
I can't imagine why they've chosen the path they have /s
Limiting 4K to specific configurations is a DRM decision, not a video quality decision. There's nothing special about 4K video: it's typically encoded in the same codecs as videos in lower resolutions (H264, H265, VP9) and basically any modern device can play it without a problem. I never had any issues with 4K YouTube videos on Linux or Windows, regardless of configuration/driver.
I think what they're trying to avoid is people capturing/copying the 4K stream, that's high quality enough to be considered a "master", and distributing it. IMO it's a pointless thing to do because dedicated piracy groups will quickly figure out ways to do that anyway, and it makes the average user experience worse. However, they are probably contractually obligated to do so.
Supporting every hardware under the sun is as simple as dumping an mp4/avi/... file.
The reason they don't support high resolution is just DRM. They will happily deliver 4k video to your underpowered Windows machine which will lag and not play it properly, as long as it uses Widevine L1 or similar.
You can argue if this makes sense or not [1], but let's not pretend they are doing this for some difficult engineering reasons.
[1] This doesn't seem to stop pirates in any way so I can't see how it does.
As I understand it, it has nothing to do with "will your hardware support it", it has to do with preventing people from saving the high quality stream to disk. Hence the reason they don't allow 1080p except on certain, locked down platforms. Pretty much every device/player in existence supports 1080p at this point, Netflix just won't allow it.
how is that significantly different from someone downloading several segmented 4k\1080 "clips" and running them? Youtube seems to be able to do it just fine.
I can't imagine why they've chosen the path they have /s