They are narcissists
According to psychologists, narcissists are more likely to be obsessed with Instagram than other people because it feeds their ego directly. A narcissist feels very good when they get followed, admired or complimented by others. (See What Makes a Person a Narcissist?)
They are obsessed with followers
Some people become too obsessed with getting followers that they become Instagram addicts. Those people feel good when they get followers, and as a result, they become obsessed with Instagram.
They want social approval
People who are very much in need of social approval might become obsessed with social networks, and especially Instagram, in order to get approval from both friends and strangers.
They don’t think they are attractive
People who don’t like their own looks might need constant reassurance that they look good. Because Instagram is all about pictures, those people become obsessed with it in order to raise their self-esteem. (See What makes a person attractive?)
They measure their self-worth eith followers
Some people use Instagram to measure their self-worth by looking at the number of followers they have. Those people become very obsessed with their followers count and so they become obsessed with Instagram itself.
They want to be famous
People who want to be famous or even celebrities usually get obsessed with Instagram because they see it as an opportunity for building audience.
They are not happy
According to psychologists, people who are not happy might always keep looking for external sources of pleasure to feel better. The less the person is satisfied with their lives, the more likely they are to get addicted to Instagram to feel better.
It feeds their ego
Egoistic people might get addicted to Instagram because it feeds their egos directly. Those people become obsessed with followers, likes and comments because they make them feel good about themselves.
They are self-obsessed
Self-obsessed and self-centered people might find social networks in general very addictive. Self-obsessed people can easily get obsessed with Instagram since it’s all about being like a mini-celebrity.
They are attention seekers
Attention seekers usually get obsessed with social networks. Instagram and Twitter might be very appealing to attention seekers because it allows them to get the attention of strangers.
They are obsessed with picture taking
Some people have a picture taking obsession. Those people might become obsessed with Instagram as well since it’s a medium that allows them to post their pictures.
People who keep changing their profile pictures can be insecure, lack confidence, and can't make decisions easily.