The biggest paradox of people who were not loved by their mothers (and they are not aware of this fact) is that they never become fully independent human beings. It's not only about being immature. It's about being a part of somebody else's body and mind. And this is the main reason these people deny anything bad happened to them from the hand of the mother. Admitting that the beloved mom, this fantastic person, contemporary saint, is, in fact, the merciless abuser is something beyond their ability.
The mechanism is simple - unborn and newborn baby is so dependent on the mother's love that he or she is a part of her body and mind. And once the love is not provided, the person stuck in this very early stage of development and cannot move on. There is, of course, a way of solving this problem by replacing the figure of the mother by someone else, by some kind of authority who supplies the child with whatever it needs. But let's be honest, no one sees such a necessity when the mother seems to be so fabulous. Besides, she would never give up on the best mean of showing off as the best parent in the world.
For the child, saying that mommy was bad is equal to disintegrating whole the world, for if she is a terrible person, he is too. If she didn't love him, he had never existed.