Maybe Google has a business relationship with the NSA. It's likely the reason Google hasn't added encryption and never will - the boss doesn't want it.
I don't get it when people keep repeating something like this. Google pushed a lot for adding TSL/SSL encryption between Google's servers and the client, to the point of inventing several performance improvements in TSL start-up. However they sure don't encrypt inside the client [note] and then sends it as a blob to server to storage, mostly because that's not really how webapps can work (for practical "can work" values). For example this wouldn't allow you to full-text-search all your own emails in gmail.
Moreover this would mean significant performance regression every time you would open up any Google web app, because the client would have to decrypt all data, without much help from indexes.
[note] Even encrypting and decrypting in the client would only help so much. It is likely they could be ordered to splice they data while in the client for any person of interest.
Cloud web apps simply requires a legal system that respects peoples' data.