Also disappointed about their promised privacy features that never made it: https://plus.google.com/+MaxHuijgen/posts/haKeEyEHR55
Yes, it'd cost money to maintain that infrastructure, but I bet there are enough people who'd want to do it, and would be willing to pay enough to do it, that it'd be profitable.
However, I suspect actual users is probably closer to 2 billion than 7 billion. ex: ~1.17 billion people use Google search.
They were never promised. It was internal dev tools that accidentally got released.