Why are many mothers so highly critical of their daughters then their sons especially if she is a single mother?

This does not apply to all mothers but I am simply speaking from experience so here is a backstory.

I have two brothers and we are all 90s kids my brothers were born in '86 and 89 and I was born in 91. My oldest brother has a different dad from a previous relationship home has been incarcerated ever since he was 2 years old and he is currently out now but he was not in his life growing up and of course my other brother and I both share the same dad who has not been in our lives much either for a different reason due to excessive substance abuse. I was my mom's favorite child because I was her only daughter and she always wanted a girl

Although my brothers and I had a very good childhood growing up, our household was very toxic because we came from a family of alcoholics and drug addicts and my mother was molested as a child by my mother's boyfriends and she also has been assaulted by male cousins and her family as well which played a huge part in her being overprotective of me.

Both of my brothers have totally different personalities and are nothing alike the oldest brother being The "Good Soon" who was always well-mannered and never talked back and didn't get in too much trouble the middle child was very rebellious, mysterious, very manipulative and dishonest, emotional and was very good at lying his way out of trouble. Whenever he would get in trouble, and was rarely ever held accountable for his actions she spoiled all of us but coddled him the most and let him get away with basically everything but I have gotten whoppings for over the most minor things.

I was not allowed at sleepovers, I was not allowed to hang out with friends unsupervised unless my mother would take me and my friends out but my mother was more lenient with her rules with my brothers yeah my mother criticized me for very small things and always help me to a much higher standard than she held my brothers even though I have never done anything for her to question my morals or integrity.
Why are many mothers so highly critical of their daughters then their sons especially if she is a single mother?
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