The competition starts from kindergarten, parents are competing with each other for things like:
1. How many English words your kid know already?
2. How many classic poetries they can recite?
3. Mathematics above requirement
etc.
It is a rat race and it is suffocating. And in East Asian system, one failed academic assessment is pretty much a failure and deemed useless, you will be discriminated in so many aspects of your life.
And it is curve based system, so no matter how hard you try, 50% will never go to college anyway.
And ofc, this system will accompany you all they way through your career as well.
People are always looking for something they can compare against, pick the winner and loser, and judge you upon it.
As a result, having kids and raising them up to societal standard costs big money, people choose to have none or one and invest everything they can to that one kid.