Because that would be the same quality. This is the internet, if an image is still recognisable after being shared five times you're doing something wrong.
Yeah OP seems to imply there's some kind of cyptographic security with NFTs. Nope! It's literally just a URL on the blockchain pointing to a regular image on a regular server.
Let me preface this by saying I don't see the value of 99% of NFTs either, but it is technically possible to make one that stores the image on the blockchain or on IPFS. Most don't, obviously, but it is possible.
I mean... I would hope not. Artists work hard to make NFTs. You should respect that by downloading the image in full resolution and quality rather then screenshotting it.