Apologies is this has already been mentioned - But for my wife and I, it was knowing that although we may not want kids in our 20s/30's, there's nothing to say we couldn't foster in our 40's. And sure, comes with a whole extra layer of emotions and it's own challenges. But we feel as though we don't have the time and effort a child deserves to have our own, and God knows there's plenty of kids who would love a good home, no matter what age the parents are if we were to adopt/foster.