DairyBox is based on a VM Scotch/Box, which is no longer supported or developed.
Scotch/Box is based on Ubuntu 16.04, whose "5 year support" period ended last year.
The solution here would be find if someone else picked-up the reigns, creating a Scotch/Box like Vagrant box based on a more recent Ubuntu, or to create our own.
At some point we will need to create our own (and I have, but I've run into problems maintaining Vagrant boxes), but in the short term switching to a different 3rd party alternative could get the job done.