For movies, the team is able to use the wide palette of the Digital Cinema P3 color space to create gorgeous teals, oranges and violets.
But then comes the time to make these movies work on TV. In order to do that, that team essentially "dumbs down" the image, removing dynamic range and limiting the color. They get it to look the way they want, given the confines of the HDTV system, and that limited version is what you get on Blu-ray or a download.
If your TV is set to the Movie or Cinema mode, this is approximately what you'll get at home. If you're in the Vivid or Dynamic mode, the TV will then exaggerate the colors as it sees fit. It's creating something that isn't there, because at the mastering stage, the director and her team had to take that all out. Is the "Vivid" version close to what they saw, or what was in the theater? Doubtful, and there's no way to know since it's your TV's creation.
Thanks to the additional storage and transmission capacities of 4K BD and streaming video from Amazon, Netflix and others, additional data, called metadata, can be added to the signal. It tells HDR/WCG TVs exactly how they should look, exactly what deeper colors to show, and exactly how bright a given highlight, reflection, star, sun, explosion or whatever should be. It can even adjust picture settings or put the TV in a certain picture mode automatically. This is a huge advancement in how we're able to see images on TVs.
The 'dumbing down' of the content to get it to work within the rec 709 color space is really the revisionism here.