When you have a child, your kid or adopted, it's a big thing. You have a big responsibility to make them happy and take care of them until they grow up. It's like...proof of how much love you have, I guess.
When they're yours, the fact the mother is willing to go through the pain, the husband willing to have someone they love go through that pain, just more proof of how much they want to have that chance, to do that.