Why do so many people seem to think that becoming a mother automatically means becoming your mother?

This stupid, overly cute question brought to you courtesy of too many pieces of film analysis that flatten out the contexts and complexities of women's lives. Obviously for lots of women becoming a mother provides a new and exciting opportunity to worry that they are turning into their mothers! This is a totally understandable reaction, considering the encircling cultural baggage. It is also a good occasion for soothing baths while someone else takes the kid so they can reason themselves out of the freakout. It is also (also) different from the trope (analytical as well as literary, alas, alas) of "You have a kid! You are now - YOUR MOM! The Cycle is Complete!!!!"

The Baby Brother: But Candide makes no sense!

Me: The novel makes sense.

Mom: The musical might make more sense to you if you'd seen the first third.

Me: Of course, when we read it for class everyone else thought it made no sense and was generally soul crushing and I was the only one who loved it unreservedly, so maybe I'm the statistical outlier.

Mom: ...You loved Candide?

Me: ...Yes?