I think the fact that it is a separate social network is actually a huge part of its draw. I use Instagram on the daily, but haven't used Facebook in a good four years.

Facebook is just too full of garbage that is irrelevant to my interests as well as stupid ads. Instagram, on the other hand, is still basically ad free, and has interesting content I care about, easily consumed without having to dig through tons of cruft that I don't care about.