It's the typical Google development cycle. Build a great product, don't get enough users, engineers lose interest and boom the product is basically sunset. Years later it is either revived or cancelled outright.
Yup, I'm seeing this with Google sites (sort of) right now. Even though they're rolling out a new version, it's pretty much impossible to get a digest of all pages on the old sites with revisions. There is an API to access this data, but it's behind an amalgam of out-of-date documentation and forgotten APIs.
