I also don't understand why Mozilla killed these projects. The original persona (BrowserID) was a pretty solid idea, but I think it's pretty expected for these things to take years of advocacy to pick up.
I wonder if it was changed and canned simply because they didn't hit their early metrics.
My (lay) reading of it was that it was indirectly killed by the FirefoxOS efforts. A lot of the enthusiastic BrowserID/Persona folks got roped into the login/auth parts of FirefoxOS. I think a lot of good enthusiasm/energy was burnt by FirefoxOS not doing well, and that burnout was accidentally/indirectly the death of BrowserID/Persona more than anything else.
I wonder if it was changed and canned simply because they didn't hit their early metrics.