Ditto that they're no good... AVNs/Games that use actual Porn, don't have much continuity and it takes me out. They have to be written around the porn pictures or use entirely different girls in different scenes. It's just messy and often feels very forced. At least other Games with their own art can cater the art to the situtation, rather than the other way around.
I generally avoid them because if I want to watch industry porn I can just go to PornHub and see the full video in high def instead of chopped up into a dozen 240p .webm files. That said I do have a soft spot for G28's games (College Daze and Power of Will) because they actually do have a great deal of thought put into them. They are genuine choose-your-own-adventure games with toms of branching paths.
There were a couple I kinda enjoyed actually, it still often beats just the video on its own due some better possibilities for self insertion or getting some kind of connection (good or bad) to a character that I won't get in simple porn. Plus, I guess there is some aspect of increasing the lenght of the whole... process.
Personally I HATE porn games with real porn in them. It just seems so... lazy? Spiritless? It just seems like it takes nothing to create. String together some images with a story? It's never coherent. There are no characters that are consistent. Just seems to lack everything I look for in a game in the worst ways.
Most porn is generic, unoriginal and unimaginative to begin with. Being limited to a few videos where the same porn actors appears and not having any control over set design, the scenes, etc. makes it impossible to make a good game based on real porn.
I don't see who the target audience is and why people keep making them, but they've been here for a while and they don't seem to be going anywhere.