I like to think that biological reasons is one of the main reasons. This is the only way to explain all of the ignorant horny people (my own parents included) that f*ck and fall victim to a busted condom (or lack thereof) and end up haphazardly having children. But they choose to go through with the birth because an abortion or day after pill isn't a desire or an available option. They are blind to the fact that the odds are stacked against them and their children will likely never become anything in life and end up living miserable lives. Children like us that eventually arrive to the conclusion that killing ourselves is the only escape from this sick, disgusting, criminally-manipulated world.
Unfortuntely for society, this demogrphic of irresponsible people grossly outweighs the people that choose to responsibly have children under financially-sound and comfortable life circumstances. And even this latter group is dwindling by the year, evidenced by the fact that D.I.N.K. couples (Dual Income, No Kids) are become an increasing trend. These people are just simply too intelligent to burden themselves with children in this dystopic day and age.
This phemomenon was best cinematically-prophecied by Mike Judge in the opening scene of the movie Idiocracy:
This is why billionaire pychopaths like Elon Musk are scrambing to fear-mongering about population decline, in order to coax the general public into procreating to keep his supply of consumers coming and justisfy his plan to migrate people to Mars and go down in history as a savior to the human race. Sick f*ck.
Baby fever is a real thing. But regardless I think it's because of past social pressure that people procreated, rather than a desire to.
I almost fell victim to this social pressure. Put off having children with my wife until she was basically too old to safely have children. Theh we got divorced. I thnk God every day that I neve had children with her. I couldn;t imgine what a pain in the ass it would be for me right now.