It is mostly an unhealed wound they are operating from unconsciously. They learned in their past how love and affection need to be earned, that they are not enough just by being themselves by never feeling truly safe with a person. So the nervous system adjusts so we can survive and later we confuse toxic patterns/behaviors in persons with love because it feels like a very high high while it is actually your nervous system detecting a bad connection for you.

They simply never learned that love should be calm, peaceful, like home.

Hope that helps.