Originally Posted by Supz

The advertising part is kind of difficult because Instagram is only a mobile app. The desktop website is not really something people use.

There could be a couple of other reasons, 1. The user base. There are millions of users on instagram. Some have facebook, some don't. A lot of people I know got rid of their facebook account since they have instagram. It is kind of like facebook but without the bullshit drama. (for the most part). They will probably be using there #hashtag engine sooner or later. It also providers more content for facebook. Since people who have both usually post on instagram and it automatically goes onto facebook. So even if the user never signs into facebook again. They are still flooding their profile with content.