I am relatively new here, not based in US, and a bit confused: why is Instagram considered somewhat a huge success in the tone of the article, that Google HAS t

I am relatively new here, not based in US, and a bit confused: why is Instagram considered somewhat a huge success in the tone of the article, that Google HAS to learn from it? There has been free iPhone Apps with similar growth before. There's no clear monetization method. There's nothing that competitors can't copy in a week. So what am I missing? Is there something I fail to see here, in the context of what makes it a successful startup?