If you like browsing pictures of butts you'll get lots of butts and of the exact kind that you'd like. I'm not sure how they do it. I don't even post on Instagram. And yet I'm addicted now to the Explore tab. They've genuinely managed to build something addictive in a way that other networks are not.
Also Instagram is completely sanitized of politics and any other hot button stuff. So its just a space where you zone out.
Instagram is the crack cocaine of social media. A cocktail of addiction and narcissism refined into its most potent form. I predict that Instagram will continue to grow and might one day rival Facebook itself.