If my network can maintain more bandwidth than needed for 1080p/4k most of the time (which it can) then there is no reason it should ever fall back to lower quality due to a short blip because you can keep several seconds (or minutes) of buffer.
For example I never have this problem on Youtube. Only Netflix.
If they can't make it work with 1/10th of that, that is their problem, not mine.
I would more prefer it would buffer more so it doesn't need to do either.
I can't imagine why they've chosen the path they have /s
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.
And just like I don't buy that argument, I don't buy their service either. I'm not going to pay for an intentionally crippled experience.
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.