This is very reminiscent of Google/YouTube circa 2006. When Google bought YT it was a small team of people and a pretty nascent product that people really loved, and the usage numbers were out of control. They left the product mostly untouched and let it grow on its own. Though there was major criticism at the time, it is one of the best tech acquisitions of the past decade.
YouTube is a content paradise though. There's tons of value there and you can sell ads against it or even charge for premium services. Where's the money in Instagram? The content is practically worthless and their only real value is in their userbase. Even though I use the Instagram client, most of the time I see photos, they come through Twitter. So that also reinforces for me that any value is in the users and not…
Preventing Instagram from developing into something that has a negative effect on Facebook. It's a "keep your enemies closer" move.