Each generation doesn't have to be bigger than the last. Two people create two children, those two children create two children, the grandparents die, the grandchildren create two children, etc.
That stabilizes the population (technically population goes down due to accidental deaths, diseases, etc. but you get the idea).
It's what leftists have been asking for: "disrupt the Western-prescribed nuclear family structure requirement". Add in the snowflake generational belief that their personal feelings trump anything else, and we get to where we are.
That stabilizes the population (technically population goes down due to accidental deaths, diseases, etc. but you get the idea).