Either the Western world allows people the financial and real estate resources to have children in the next 5 years or we're all fucked. The tail end of the boomers enters retirement in 10 years and while millennials can take care of the boomers, eventually we will need to be taken care of, and for that millennials need to have children now as long as we still can.
Economics could as well and the system would still work.
Why is it impossible for Americans to live with 300 sq ft per person like baby boomers did as kids, but now we must live with 600+ sq ft per person?
Because the American suburbia developers want some nice chunky profits. It isn't enough any more to sell glorified matchsticks and cardboard.