I think what happens is that other attributes that they’re attracted to make the person more attractive to them, so that they aren’t weighting solely physical appearance. As in, they might not choose to hook with that person, but would still see that person as a solid choice for a life partner.
That said, it’s horribly cruel to get into a relationship with someone that you have zero sexual desire towards, unless that person has no sexual desire at all. You may not be physically attracted to them, but you should still desire them sexually.