I designed the data centre network for one of the largest streaming platforms at the time, around 12 years ago and back then, one problem was the amount of bandwidth required to stream all of the different formats (sd, hd, 1080, iphone, TV, ipad etc), especially from the CDN perspective.
The bitrate for 8k is so much more that nobody really wants to handle it at scale, everybody streaming native 8k content would absolutely smash CDN and infrastructure bandwidth, for relatively little gain when it's difficult to tell the difference between 4k/8k.
Then there's the production side, filming it, storing it - editing it all at 8k native is not trivial, it's hard and it's expensive - so nobody really wants to do it.