Because it's extra work to make it open source and few outside of Canonical are interested in contributing. Open sourcing an existing component and maintaining it as such has non-trivial overhead. In that case that work is better spent on other, higher priority items. My guess is that they've gauged that the cloud end being open source won't move the needle on who uses Snap and Ubuntu so they've deemed it low priority. Personally I'm using Debian and Ubuntu and therefore Canonical has root on some of my systems. Given I can implement a cloud end for Snap, it bares very little importance to me that today the cloud end isn't open source since it's run by the folks that have root on my system anyways as well as supply all other packages on my Ubuntu systems. In fact we don't even know what the cloud end for the apt repos is. It could easily be Sonatype Nexus. For me the important bit is the client and installer side of Snap since I can't implement that in a relatively small amount of time. :)