I don't understand the surprise people are experiencing from the revelation that Google and Microsoft scans the stuff you upload to their cloud storage systems.
You are literally giving them a copy of your files, and generally speaking, you also agreed to allow them to allow them to scan your stuff. Google Drive's terms of service explicitly states that your stuff will be scanned:
"Our automated systems analyze your content (including emails) to provide you personally relevant product features, such as customized search results, tailored advertising, and spam and malware detection. This analysis occurs as the content is sent, received, and when it is stored. "
Why would anyone reasonably think that their stuff is somehow private when it's in the cloud?