Mother's aren't magically gifted with perfect parenting skills as soon as they become pregnant, if something is missing in their psyche it isn't automatically filled.
I'm sure your mother couldn't give you a proper explanation so it is impossible for strangers.
You have done remarkably well and should be proud of the adult you have become.
Give yourself true peace of mind by accepting the simple fact that your mother is a flawed human being as most of us are and you are no way to blame for the way things are.