Gameplay already takes priority. But they are telling a story. In order for that story to make sense, certain things have to happen in a certain order.
As for the *porn* aspect? It's very common for porn to have to be unlocked. It has *long been* orthodox for porn to have to be unlocked, going all the way back to the OG visual novels of the 90s. The fact that some games don't do it doesn't mean it's wrong to do it.