Some can't. The parents themselves have been indoctrinated or traumatised to the extent where they can't control their actions.
For example, addiction. If you are an alcohol addict, you can't just quit alcohol. You literally go insane because of withdrawal. And when they are drunk, they abuse their children.
Or other people born with disorders. A person with Borderline Personality Disorder or Bipolar Disorder can't control their emotions very well. It's not simply a matter of "you choose to". There are many things that you can't just choose to do. You may find a way to solve the problem but the damage is done.
That damage is fate.