It satisfies the desire of vanity for the consumers.
When you purchase an NFT it means people will acknowledge (backed by the blockchain) you're the only person in the world to "own" this particular item.
The need to create NFT is to get money from whatever you created, if there's anyone find it interesting and wants to "own" it.
I'll give you that it does allow creators to extract value from their work.
I think people are being sold the idea that they're buying a certificate that proves they own (in some sense of the word) the artwork, but in reality they're being sold a certificate that proves they own the certificate.
For real legitimacy of the source, you need either the author or a trusted third party.
To get copyright protection on something you may need to hire a lawyer, file some papers etc.
Maybe NFTs are more similar to a combination of letters of authenticity and a deed when you buy a painting or something at auction stating that the thing you have is real and that you are the owner.
There are indeed exceptions, but I doubt any of those exceptions are going to care about NFTs either.