My father used to say people like this have a need for constant reassurance. As others have pointed out, they NEED to feel wanted, loved, appreciated, etc.
I have a co-worker like that. Quite honestly, her life is a mess, she's people pleaser, and wants everyone to like her. So she'll do stuff like giving customers what they want, even if it means bending the rules (she's a manager), and so on. While I don't have a problem with one question about her new hairstyle, when she asks 20 times, its like trying to appease a 5 year old.