So the marketing company or the sales dept turns up the juice a little bit. They allow them to stand out a little more. They give them special bells and whistles the user created content doesn't have. They let them animate, float over content or auto play video or sound.
Why? Because it makes the product a little better for the customers: the advertisers. Instagram, just like their Facebook overlords, are now in the business of making their product as good as it can be for the advertisers while keeping the users just happy enough not to leave.
I really dislike this cycle in the startup world. I don't know a good way around it. I'd like to see someone disrupt that.