Yes, I don't think this is a single faceted issue. I've yet to see anyone here mention animals yet... but numerous animals in captivity have also been shown to have far lower breeding/fertility rates. Factors like restricted space, lack of mate choice, and disrupted natural instincts can all influence animal behavior, and I see no reason why the same can't apply to us?

I know for me personally, it's not economic reasons as to why I have not had children, but more a problem of finding the right mate at the right time. Some people just aren't socially fit for each other...