The short version is that to be a viable project, Mitro really needs at least one person who is very passionate about the possibilities of an open source password manager, and is willing to dedicate a significant amount of time to improving it. We haven't been able to find someone like that to really take it over yet.
The longer version: we spent two years trying to make Mitro into a profitable self-sustaining business, and we couldn't get it there. We had hoped that we could figure out a way to make it a self-sustaining open source project, but I think we vastly underestimated the amount of effort it would take to do it justice. At this point, we have somewhere between 5000-6000 active users, which is pretty insignificant (LastPass and 1Password have millions). I'm proud of what we built, but unfortunately easy password sharing and organizational tools to manage passwords were not enough of a distinguishing feature for us to find enough users to justify continuing the company.
Open sourcing the project is a last ditch effort to try and keep something of what we built alive. Sadly, it turns out that maintaining the public service is also a fair amount of work, so we need to find someone to take it over, or it is likely that Mitro will be shut down in 2015.
Evan