If love is blind then why is lingerie so popular?

That's part of what 'love is blind' is about. We first see the outer packaging of a person and then we generally like what we see and look at the person more passionately, but part of falling in love is getting to know the inner part of that package (the inner self of that person.) Sometimes people make bad mistakes because they fall in love with looks and they don't see the danger signs that their so-called true love is emitting from every pore of their being. In time we often find the inner self of that person is pretty ugly.