Why are some people unable to apply the lessons from their meditative practices?

Yes, I may be cherry picking the data. But I see some people in my life - who are committed to meditation, bettering themselves, yoga etc - that are somehow unable to apply their practices to their lives. They end up strongly identifying with their thoughts leading to depression or lashing out at others. What is the force in play when this happens? Is it a lack of willpower? Or self awareness? Of course, there are people who take great lengths to battle their trauma and are committed to using meditation to better themselves and to be kinder others. There are also very ‘zen’ people out there who haven’t meditated at all. I’m thinking of my mother in particular - who practices meditation daily and actually encouraged me to pick up meditation. Yet, she can be extremely defensive and emotionally immature, and it is bewildering to me.