So, i played this game, and while i share the same feeling as this is just too short, i must give credit to the author (Who is chinnese, not japanese) for trying to grasp around this fetish.
I think the main reason it has so little material, is because the author risked money and time at developing this.
If you look at their games, author has a single art style for these games. However, this last one looks like it was commisioned as it's a much better art than what actually is seen on other games. And looks like it worked, yes, as ironic as it seems, this game sold, and sold a lot in comparission with other NTRworld games.
I follow NTR in Twitter and Pixiv, and has announced QOSMILF, same theme, but with a mom getting blacked by her son's black friend. However, from what author has posted, this new game is gonna be larger and have more things.
NTRworld is pretty chill, they will answer if you ask. And is currently asking for a translator for QOSMILF.