Flash games were some of the first porn I came across as a kid so even though the first games were super simple and often just topless stills or something it was super exiting back then.
The ability to interact with the situations can help with immersion. VNs are a bit different since you are usually just reading a story but the ability to occasionally shape how it plays out is nice.
I enjoy the art and I love the type of characters stories that people come up with. That mixed with i've always been a sussy person makes it something that is perfect for me.
Newgrounds is how it started as for why i like porn games it's mostly because i like being put in the mood for sex with some foreplay or maybe even story (and god knows porn actors usually have terrible scripts) so i ended up finding porn comics and porn games to work great (porn stories lack the visual aspect)
the taboo nature of the themes in the games. Irl incest is fucking gross and immoral. Fictional incest? Let me fuck the mom, daughter and youngest daughter all at the same time
I've always been attracted to porn with a plot, and here I can not only see the plot, but also influence it, which is much more interesting than regular porn, which is why it immediately caught my attention.
Newgrounds for me too (any old folks on here remember when Pico made his debut?) as well as seeing ads for games like Leisure Suit Larry (which I still haven't played it). I love a good Sierra point and click game and if I can solve the puzzle the developer had in mind and it unlocks boobs in the process, I'll spend the weekend beating that game.
Two things. First, I enjoy a good story. With regular porn you either get a production with 3 mins of really bad acting then watching people have sex, or amateur videos that cuts straight to the sex with bad angles and a fake title as the closest thing to any semblance of context. Neither was cutting it. This led to porn comics and hentai.
Second, I already loved playing video games and the interaction and immersion you get with them. In addition to a good story, I'm the one affecting it and changing outcomes. I found out that the two concepts could be combined and the rest is history I guess.
(Slight tangent / rant) Strangely enough, even though I like reading hentai, I detest linear visual novels. I don't care what anyone says, they just aren't games. I'm sure lots have great stories, but they don't have any interactions and therefore should not be considered games.