World population in 1756: ~650 million
World population in 1879: ~1.6 billion
World population today: ~8.016 billlion
...so obviously the problem isn't a matter of not enough people.
Actually the fact that people who are just so fucking beyond-the-pale stupid, mediocre, and unequivocally unremarkable happen to be the richest people in the world today has a lot more to do with it than birth rates... I mean Musk is proof-positive that this isn't a meritocracy.