You made a promise to your wife not to sleep with anyone else. Everyone knows why that pleases her, and what purpose it serves. Your wife is not God. You are being faithful to your wife, not God.
Mary was being faithful to God... so Mary... made a promise to God... not to sleep with anyone ever, even her husband... why? when? Why does this please God? What about poor Joseph?
You think that any sex - God, even marital sex which isn't a sin even according to your own religion - would displease God somehow and make Mary dirty and not perfect anymore. Oh yeah, you don't have a virginity fetish at all, sure.
Since you brought it up, did Mary magically not inherit sin like all the rest of us humans did? If God could let her do that, why not let ALL of us? Ohhh, because it's not in the big complicated plan of punishing us for something we didn't do by making us inherently sinful and then saving us from that sin, but not all of us, and only if we believe a really bizarre story, and only after a bloody horrible sacrifice that God needs in order to forgive us. You know, that complicated plan that's totally necessary for... for... um... well, I'm sure it's necessary for some reason!
Anyway, the point is, the virginity fetish of Abrahamic religions, which is totally clear to anyone who isn't a participant, is why it made sense to have a picture of Mary, the quintessential Holy Sexually Inexperienced Woman, up when talking about the "restoration" of virginity to fool your way past a ridiculous antiquated misogynistic requirement.