They weren't weaned well. When we're born, we attach ourselves to the Stomach channel of our mothers at the breast. After a time, we develop our own stomach channels and we are weaned. Mom and dad are also in charge of emotional nutrition as well as the kind derived from food. Mom and dad's support and nurturing are required by the child because it has not yet developed the ability to provide himself or herself with their own self-esteem.
Some people eventually do mature to the point of becoming emotionally self-sufficient.
Many do not. For those who do not, their earth element cannot mature enough to properly nourish their metal element and an emotional neediness becomes pathological. Emotional neediness and attachment go hand in hand, just like mother and son. Middle jiao deficiency also leads to the formation of damp and phlegm. It can be described as the inability to understand your place in the world, or your place with yourself.