They want the convenience and respectability of a marriage or long term partner, especially if that partner makes life easier for them in so many ways and they want to be able to indulge themselves and fuck around. It’s called having your cake and eating it too and it’s rooted in entitlement. He’s taking away his wife’s agency and he doesn’t care because he comes first. I’d say he’s a narcissist and watch how quickly good guy Bob morphs into angry Bob or self-pitying Bob if his wife ever enacted any consequences. Bob is a self-serving man child.