Instagram was never going to "sell your photos." If you read the TOS, they were reserving the right to advertise against your photos much like how sponsored stories work on Facebook.
But advertising is so evil right? Time to give up Google Search, Gmail, Google Maps, LinkedIn, New York Times, etc.
Frankly, I find it funny that your everyday consumer is in an uproar because they think that their kissy-face photos could even be sold.
Companies like National Geographic whose businesses are built on the IP around their photos have legitimate reasons to be concerned in general. In this case, though, these changes would've allowed them to advertise their magazine on Instagram. Professional photographers may also want to protect their content from being used in advertising.
But 99% of users are every day people taking pictures of babies, dogs and the sunset...content that would almost never be "sold."
Also, the fine print on AppData shows that their method of measuring users is completely prone to error. Many other apps showed a drop off and FB made some algo changes around the same time.