They don't know how to or don't feel the need to take care of some of their own basic needs, especially if there is another person to care for instead. Codependent people are addiction prone. They may drink too much, shop too much, eat too much, etc. Dulling the senses is a great way to avoid knowing yourself and dealing with your feelings. Intimacy is avoided.
Intimate behavior requires familiarity and comfort with one's internal world.
Since the codependent person regards ordinary human needs as shameful, embarrassing, dangerous, or otherwise uncomfortable, meeting basic needs are often dismissed. Any relationship that ignores the self is superficial. They control their self-esteem by catering to others' needs. They control by their over-responsible performance, picking up where others leave off. They control by avoiding intimacy or by clouding the mind.