Porn scenes without a real script are so 1980s. It was easier then with less competition. Today with so much available, if you want to sell has to be better.
Mos porn buyers have a bunch of favorite fantasies, play them out and it stimulates them to buy. Play the same fantasy out time after time on the same site and eventually it loses appeal and can become boring.
I shot one scene from Manwin. Girl playing herself going to work, as a porn model. Relating to the viewer. Then going through her show all the time teasing the fuck out of the viewer to a few climaxes. Then at the end shooting her panting and sweating to show it was all for real. Nothing hard or difficult about that. Cherry will tell you how bad it was.
On the Tube it was given away for free on, votes were good. In fact very good.
So why isn't it done more often? Shooters have to churn out to many in a day for too little money, models not bothered and shooters not able to motivate them.
Some sites get it right, some don't. Your conversions and retention ratios will tell you which ones.