Any ideas why this exist and or who buys this stuff?
Well, much like your username, this is actually a really good question.
There is a ton of gear on the market which is designed and built for the movie industry. While we live in a world of $1,000 cel phones which sound expensive, but encompass so much, including our video and photo taking capabilities, when you get a digital SLR camera, from someone like Nikon, you may find that you drop several thousand dollars to buy a lens, or several, for that camera.
Then you step up to movie production cameras, and you find out that a cheap lens is $20,000 for their cameras.
WHY? WHY!!!????
Because the lenses offer certain features and functions which are otherwise unavailable on consumer grade cameras. The optics are significantly better overall with extremely high precision, but the actual design allows for many things which consumer lenses don't offer. These features can actually be looked up on Google and there are YouTube videos which discuss the differences between a cinema camera lens and a consumer camera lens. Yes, the cost is significant and the features offered are unique.
The same is true with actual professional level gear. This isn't consumer. It's not commercial. It's designed for professional use and professional video editing and review work. The type of editing work that is done for multi-million dollar films. Think, "The Avengers", and think about 20 or 30 film editors all working on their own consumer video monitors. The color of all the monitors isn't the same, the quality isn't the same, etc. Then, when you watch the movie, every other shot looks completely different and the final result looks like garbage.
Now, you stick a $40,000 4K monitor in front of every single one of those 20 editors, at a cost of nearly a million dollars in monitors, but you end up with a result which is absolutely top shelf. These monitors aren't just a single expense for a single movie, but are part of the studio's editing suite. These studios spend millions of dollars for properly calibrated and very accurate monitors, good cabling, top shelf previewing facilities, etc. and it dwarfs any typical home gear. They also pay the money to have this gear regularly calibrated so that everyone sees the same thing.
I get it, it sound crazy. Until you think about the amount of money which is on the line. A franchise like the Marvel series is worth billions of dollars to Disney. The importance of maintaining such a demanding high standard is only possible by ensuring that the absolute best, and most accurate equipment is used throughout the entire filming and editing process.
Oh, and as an aside, there are mice which cost thousands of dollars. Why? Because they are genetically identical to each other. This is something labs use for drug testing to ensure that all test samples are 100% identical. A variance from one mouse to another wouldn't yield accurate results. Once again, sounds crazy, but in the name of doing things right, this is the reality that science must deal with.