Not understanding might not be far from the fact, but it is probably just posturing. I doubt most of the Tubers understand it themselves which is the real reason they can't share. They saw it on some other YT video, and then made it like it was their own idea.

I've tried to explain how to use waveforms/vectorscopes and why they are important. Those things are rarely used any more, and people just don't realize how much more difficult they make it on themselves by not using them. Just because you can push that knob to an 11 doesn't mean you should. Pushing that knob while looking at the scopes will tell you when to stop. This was life or death when making content for broadcast.

Also, I've seen all sorts of weird things that blindly applying a LUT wouldn't solve. There was a specific Red camera in town that had a very strange issue where the green color channel was not recording correctly. One shoot we had footage on was of an ice cream type place that had lots of whipped cream on the desserts. However, as you pushed the levels up, the green lagged behind so as the red and blue channels were maxing out the color on the screen went magenta. Applying a LUT would have looked terrible, but the colorist was able to go in to adjust the levels of the green channel separately so that the cream went back to white. It saved the shoot because a camera was not working properly.

There's also interesting tricks to do like when shooting through windows of a high rise will give a green tint to things. So lowering just the green channel will bring things back which could be a specific LUT, but the thing with LUTs is they tend to get used for the wrong reasons. Shooting underwater without a filter can also be dialed back, but it's specific to camera/depth type of situations.

Another common ask was to "open up the eyes". Well lit faces are notoriously hard as the sunken eye sockets just naturally shadow. So you add a window to the eyes and push the exposure up to achieve the effect that no LUT will ever achieve. If the camera moves for a tracking shot, the windows can track along with it. No LUT will ever accomplish that either. The eye is naturally attracted to the brightest area of the screen, so there's ways of grading something so that it suddenly receives some attention that a LUT would not get there, again using windows. Some of the internationalization of releases have small forensic tells in them to indicate which locale it might have been leaked from. One specific example was a stack of towels in the background of various colors. Through color correction, they changed the colors of the towels to be different for each region.

So so so many things that well graded footage can have done to it that "you wouldn't understand" but would never come close to achieving with a LUT. Wouldn't understand is very harsh though, and is a total cop out from someone that sounds very pompous. I would say "wouldn't consider" as something that could be done let alone needed to be done.