Why does a Godparent need to be married in the Catholic Church?

This question has really been bothering me.

My husband was chosen to be the Godfather of our niece, I’m not the Godmother. We weren’t married when he was chosen. We’ve since been married, and we’re just waiting for the baptism of our niece.
Well, we were infomed that because we were not married in a catholic church, that my husband cannot be the Godfather.
I don’t understand this. Do they mean that if I were the Godmother, we’d have to be married in the church?
Also, this may be silly..but does getting married in a catholic church just mean we didn’t have a catholic priest sign our marriage certificate?
Why are they so strict as to who can be a godparent?
My husband says I’m taking it too personally, which of course I am, but I feel it’s an attack on my marriage. I don’t like the fact that people seem to view my marriage as invalid, just because a priest didn’t marry us, and because we didn’t take those classes. I think it also upsets me because now it makes sense why my husbands family didn’t really acknowledge our marriage…other than one Aunt giving us a nativity set as a wedding gift. we got married in august….i’m not religious at all…it will go down in history as the weirdest wedding gift ever