Let's be real, after a project is finished, no developer is going to randomly keep watching the docs page of one of the probably many APIs they used for it.
But they also were emailing - I got like five emails for my personal projects warning me that things were changing. Plus it was reported in the tech press:
http://www.macrumors.com/2015/11/17/instagram-new-api-change...
http://techcrunch.com/2015/11/17/just-instagram/
I'm really not sure what more people expect instagram to do.