Snaps bundle their dependencies, which take time to fetch and unpack, and they’re typically made up of multiple parts, each of which need to be built and installed into the snap. Once you finish this process, you need to install the snap and test it out. Once you notice that your code is terrible and doesn’t work the way you thought, you have to make a change and go back through that process again....
Part of the snapcraft CLI’s development roadmap this cycle includes the ability to build snaps on distros other than Ubuntu. Part of that work includes investigating each plugin to determine if it’s possible to get it working on other distros. As a result, I’ve been looking into the Catkin plugin recently, using Fedora 27 as my proving ground (since that’s the distro with which I’m most familiar after Ubuntu). The first thing you’ll notice trying to get ROS working on Fedora is that, unlike Ubuntu, where Open Robotics maintains infrastructure hosting a repository of Debian packages, there is no repository for you to use: you must build ROS from source....