Seems obvious to me. He can get the sensation of pumping away in a wet fanny at home. What he's paying for is what his wife won't give him, i.e. the feeling of having a living sex doll to play with, who won't judge him no matter what he asks for; feet licking, bum sniffing, dirty talk, licking her while she stands over him like a goddess, whatever... He's paying for being able to express himself sexually with someone who'll do what he asks and smile lovingly at him while she does it.
He's paying to play, so up to him what he chooses to get for his money. Maybe they have a part 2 where he actually gets stuck in. I would love to play with her.