I can explain this - a lot of people miss the point of NFTs so I can illustrate the value here.
Buying an NFT is kind of akin to buying an autographed photo (so in this case, the person has paid the money to buy a signature from the person who shot the clip originally).
If you buy a signed photograph from Taylor Swift, you don't own the rights to Taylor Swift, her likeness, or even that photograph - but you still have a photograph that Taylor Swift herself (probably) signed. You don't care if someone else uploads the same signed photograph of her or she sells the same signed photograph to thousands of other people. It doesn't matter - because you wanted a signed photograph of Taylor Swift.
Would anyone really pay $760,999 for a hash that references a YouTube clip and expect that they then "own" the video because they have the hash? Of course not. No-one is that naive. They just really wanted an autograph from the person who made the video, and thought their signature worth $760,999.
Does it matter if it's not worth anything to anyone else? No more than it matters to a Taylor Swift fan if other people are not as excited about the photo they could have looked at for free but decided to pay $760,999 for.
As long as the buyer is happy with the autograph, and the understanding that it provides no rights whatsoever and is likely not worth much to anyone else, what's the problem with them spending SEVEN HUNDRED AND SIXTY THOUSAND AND NINE HUNDRED AND NINETY-NINE DOLLARS for an autograph from the Charlie bit my finger dad?
Now, you may think to yourself that almost $800K USD is a bit much for a single autograph from a person that shot a YouTube video one time that got popular by random chance, but you have to remember that no matter what happens that buyer is going to be telling their grandkids one of two really interesting stories on their deathbed that both centre around that autograph.