They could also be using the porn games just to show ther skills in art, writing or programming. A NSFW work portifolio.
For example, Kiniko Nasu, of the Nasuverse. Creator of Tsukihime and the Fate series.
His visual novels at first were porn ones... but if you did play them you would see it was just two or three scenes per route, that could easily be removed with no loss, with A LOT of interesting story in-between and even comedy segments after game-overs.
Nowadays people are even surprised Fate/Stay Night had porn scenes (as I said, they would be easy to skip with no loss... which is what was done in the Realta Nua release for PS2). There is no scene in Fate/Extra games, and while there are mentions of more mature materials in Fate/Grand Order, a couple of events like the two Beast 3 ones being focused exactly on the aspects of love turned into sexuality, it is just a few crude words and innuendos, there are no visuals or actual sex scenes besides the characters wearing skimpy clothes.
So while some may be like you said, others are just using the porn games to be able to work in other areas later.