This was proximately caused by Snowden disclosing what the NSA was doing. It was ultimately caused by NSA monitoring major swaths of the population.
ETA: decent summary: https://en.wikipedia.org/wiki/Proximate_and_ultimate_causati...
I’ll still argue for ultimate cause because if it wasn’t Snowden it seems likely would have been someone else.
I’m a firm believer in don’t shoot the messenger, even if they are flawed.