Miro started Mambo as a part of their business back in 2000, IIRC. The following year, to help get greater input to Mambo, it was changed to an open source project. 4 years later we now have an award-winning program. Miro set up the Mambo Foundation to oversee the project - a wise decision, ensuring that a structure of healthy and practical management and accountability is in place as well as keeping Mambo independent of Miro.
What has gone wrong is: (a) the leadership of the Mambo Foundation happen to all be on the paid staff of Miro, which puts into question its independence, and (b) that none of the development team were invited to be part of the project's management. Not one of them.
A saying we use in the UK is "someone moved the goalposts."
The result is the wholesale departure from Mambo of the development team, along with a copy of Mambo, which, being open source software, they are allowed to do. Looking at the number of 3rd party developers announcing allegiance to the Joomla! version and the 4,000+ signed-up members to the Joomla! forum, the vote of support for the team that has developed Mambo over the years continues with the software that as of 1st September is now known as Joomla! Miro will continue to develop Mambo using a new team of developers, although inevitably Mambo and Joomla! will become quite different as new versions are released.
That's as I understand it, although you may need to be a bit older than five to understand this!