A social network's ideal audience would be a group of people who are relatively discontent with their lives and provide a series of small improvements to that state of being, but ones that quickly fade, and then encourage them to repeat that cycle as often as possible. That way the susceptibility to advertising remains high and boosts advertiser ROI, which raises the social network's value as a platform.
Come to think of it, that sounds pretty familiar.
I've never used Instagram much, but that sounds like one aspect of that network I've read about. Everyone curates their profile to make their lives seem more fun and more interesting than they really are, often with a materialist angle. The real you looks inadequate compared to these false lives, leaving many feeling insecure about themselves. Then you have professional "influencers" with hyper-curated profiles that depict a fantastically fun and fashionable life. They make money by shilling products that subtly promise to let you join in on that lifestyle, if you only buy.
Its just that, Instagram especially because of the power of an image, its like not only did they set out to create a platform to maximize your insecurity, they recruited thousands of people and gave them a special title ("influencer") and pay them to amplify that message as loudly as possible, then bake in the same addictive interactions as Facebook, and then monetized the whole thing.
Its not to say that its always bad and should be shut down, just be aware of the effects it can have and be honest about how you react to them.
Success for a social network is not "people feeling better on average" it's people coming back more often on average. Their actual level of enjoyment or well-being is irrelevant to the platform.