There are many reasons to lack confidence. I know many women who have been heavy their whole lives. Women who are much taller than average and can't find dates because of it. Women who aren't considered attractive by modern standards.
Many of them have learned that their worth is not based on their appearance and, therefore, they are genuinely confident.
I don't think it's any different for men, especially since men are not judged nearly so harshly on their appearance - case in point you're married. I have several heavier friends that have never even been in long term relationships.
I think the bigger issue is that we are not okay simply being alone. Being married and having children is not the be-all and end-all. There are many different paths to be happy and successful in life.
In fact most of the people I know who are married are miserable. So why do we put relationships on this pedestal that they clearly do not belong on? Being happy and confident in your own skin should be the goal. Then if a partner finds their way into your life, it's a bonus. Putting all of our value on being partnered up is the real problem here.