There is a difference between sex and love. Maybe his wife isn't able to have sex because it hurts, but still loves and cares for him.
It isn't always as black and white as people outside the relationship may think. There is also a sense of security in marriage. If he's ill she is there to take care of him. He isn't alone. Hiring a girl for just an hour isn't going to love and care for him the same way. And after years with someone, sometimes it's hard to imagine what life would be without that person.