NFTs are stupid and awful ideas, but I suggest actually reading up about how they work so you can more accurately shit on them instead of repeating things you read on twitter.
That's the entire point of a blockchain. It's valuable because other people agree that it is. Of course, the actual JPEG can be copied, but that doesn't mean your blockchain ownership of it does. You are kind of shouting dibs, but the difference is that a lot of people care. And as long as someone cares enough to pay you money for your dibs, then it has value.