I used to work in porn around when these games were the "hot new thing" for the porn creators. The games are not made by normal video game companies first of all, they are made by pornographers along with a team of programmers. The real reason that these games exist is that they are the only ethically means of getting data on porn viewers ejaculations.

I'm sure you've seen the ads for games with scantilly clad animated women with the large flashing "try not to cum" logo. It has become so ubiquitious to see "try not to cum" on the advertisement because that is what the pornographers want you to do. Try not to cum, and when you do cum you continue playing the game. Before these games, there was no way to determine how long someone lasts when watching porn, but with these games, the game time and the interactions of the player are logged into an algorithm that determines how long it took you to cum, how long you physically came for, how many times you came, and even how many times you came close to orgasming but stopped yourself.

Each time you play the game, there are different "visuals". Also, based on your click speed, and other variables, the game can determine when you are about to orgasm and sometimes will immediately play a much more niche porn category so as to collect date on more obscure porn that wouldn't normally be in the game and to log the players reactions to this "bait and switch". So yeah, these NSFW games were the invention of pornographers who wanted a way to log data about users cumming. The data is then sold to advertisers and other pornographers.

Some developers have even changed it around. And actually measure the time it takes the companies to cum while fucking their customer. EA has been investing heavily in this tech over the last few years.