how does society even work nowadays?!?!
It does not work. Society is already collapsed. People are stomping on each other. Almost everyone see only their own good, and they do not care about others. Only a few people care about others. I would not call this society.
Why is the world population not shrinking?
The world population is increasing. Why? Because people are stupid. Just take a look at Africa. Huge, deep poverty and misery, and they give birth to one child after another. They seal their own fate. And humanity in general behaves like a virus. They ruin something, then they move to somewhere else, they ruin that also, and then they move to somewhere else again, and the cycle/circle continues.