I’ll focus on just 1 part. Why porn is legal and prostitution isn’t in the United States. In short it’s the power of the 1st amendment. The camera and all that means that it can be classified as speech/art. At the same time it doesn’t meet the very high standards for limiting speech. Anti porn People have tried repeatedly to ban it but they’ve so far failed to come up with a version that isn’t considered to violate the 1st. Prostitution is much easier to ban because it doesn’t have the 1st amendment protection. People/the courts aren’t worried about the ramifications that that would have. There usually appears to be other arguments in favor of legalizing porn but in the USA the 1st amendment seems to be by far the biggest reason why. Now you can look at as just a technicality that makes 1 legal but not the other but it’s the implications and precedent for what it means beyond that 1 area that makes that small difference so important.

It’s worth noting that it’s legal to view but state laws and such make the production of porn for sale subject to a lot of regulations so there is more to it then the difference simply being whether a Camera is on.