Those of you who want sex less frequently than your partner, why not let your partner get their fill elsewhere?

I don't necessarily mean couples where one person wants sex 6 times a week and the other person wants sex 7 times a week. I'm thinking more of those couples who have sex once a month or less, despite one partner wanting sex more frequently. This notion of "I don't want to have sex with you and I also don't want you to have sex with anyone else" boggles my mind.