What AI upscaling (and generation) shares with the examples in the article is the strong denoising process (commonly referred to in video discussions as DNR, digital noise removal), hence why films like the infamous 4K version of Terminator 2 look so 'waxy'. In T2's case at least it's because it was based on the 3D version of the film (required such denoising for the stereoscopic process).

There are three sizes of Ultra HD (4K) Blu-Ray discs: BD-50, BD-66 and BD-100, with the latter two seeming the most common ime. Various releases, particularly if the run time isn't excessive, will encode them to fit on the less expensive, smaller capacity disc (IIRC BD-100 is harder to manufacture due to tolerances).

The other aspect is of course streaming/online digital encodes, which always optimize for filesize. One comparison of half a dozen 4K streaming services by a user on the enthusiast Blu-Ray.com forum found iTunes was about tied with the highest peak bitrate (~31Mbps), which is still only about 1080p Blu-Ray bitrate (Ultra HD Blu-Ray by comparison can be as high as 90Mbps).

What's ironic is when a film is released with the original grain very clearly intact, like Blade Runner: Final Cut, I've seen some comment their other family members have thought there was too much grain (tbf there are some very grain heavy—but lovely—scenes).

I think the effect of years of smartphones auto denoising all photos has contributed to some of this lack of pushback by non-enthusiasts.