Instagram is part of a huge corporation though, owned by Facebook. Nobody pays for it on any platform. These huge corporations are different than small time independent developers.
Agreed, but in the case of Facebook you pay with your personal information. For them i can imagine they need to weigh up how much money they can make from an awesome app on windows phone vs spending time on other features for other platforms to keep a larger amount of people using their service and not jumping ship to something else. I see it at work all the time, I'm the frustrated developer wanting to do all these cool things for the users bite don't control the money, managers do, and they generally only look at ROI (and half the time don't even understand what it means...)