I was going by what the video provided. Just because you can provide an example of a movie which was processed at 4K doesn't disprove that 4K is still not overwhelmingly embraced by Hollywood. Even your asking about the cameras seems to support the argument that the production chain hasn't changed to 4K yet. It will, or it will move to a higher resolution eventually.
Is this list unreliable:
https://referencehometheater.com/ultrahd-blu-ray-title-info/
?
Because there is listed about 200 uhd titles that had 4k DI.
I posted that link to that article about Light Iron, because it tells a bit more detailed story than 2k vs. 4k. Even if the article is 8 years old.
Because these aren't the only options.
And it's really sad thing that something that is posted in 3.9K is listed as 2k.
Working with frames that are 4096 pixels wide tells nothing about how much
angular resolution or
spatial resolution the frame really have.
There was like a decade when so few movie theaters had 4k projectors, that using about 4k in the post to have something like 10% more real resolution was just not worth it.
But what people really see when watching uhd-disc?
Pixel dimension of the frame is 3840 px wide.
Then almost all people watch it on a display that overscans about 5-10% of that away.
You do know how much real resolution is wasted when you scale those remaining 3456 px to screens 3840 wide picture with consumer grade televisions realtime conversion?
Why this happens? Because almost nobody knows what 1:1 setting in deep down od the display settings of the tv means. And if they find it and try it they see all kind of garbage when watching broadcasted signal. So they don't use, even if they could find it.
Lets say that movie is shot with 5k sensor, which is debayered to 4k picture and has 1500 cycles (with decent MTF) of resolution after LPF.
Then you make the post in 4k and scale that to UHD, which drops real resolution to 1200 cycles and then overscanning in tv drops it to about 1000 cycles.
Another movie is shot in 3k after debayer and has 1100 cycles. Scaling to UHD drops it to 900 cycles and overscanning to 800 cycles.
The difference is not huge.
Then if the 5k camera material is a bit soft, because of hundred of reasons, including that director, dp or editor likes it soft and 3k camera material is really sharp, the end picture, which uhd watcher is watching can be pretty much the same.
People making these movies are not stupid. They are not making decision about some numbers just because of the numbers. If they gain very little by bigger number, they use their money where it counts. If that some 100 cycles of more resolution in uhd watcher's tv costs $50M, they could use it somewhere else. Maybe shoot 20 days more. Or double the budget of set design. Or vfx. Or just marketing.
For short: that picture pair on wikipedia's page tells about everything:
1.2 Spatial resolution