Ok, I’m friends with a reasonably famous porn actor - if nobody pays for porn there will be no free porn.
Shooting porn is time consuming, and expensive. A full length video can take a day to shoot, and then several days to edit. Not all actors are decent filmmakers so you may have one or two additional people behind the camera as well.
Then there’s also the equipment costs. Recording equipment, laptop for editing, sex toys etc. That stuff does not come cheap if you want to make good porn.
Actors have bills to pay. They have to eat. If they’re not getting paid they’ll stop doing porn and go back to being web developers or hairdressers or doctors or whatever they used to do before.