ccsm (CompizConfig Settings Manager) is just a single tool of the entire compiz compositing manager. It's an optional tool, and a power user tool at that. Thereby, since tags are designed to make it easier to track questions users are interested in compiz developers probably don't want to follow ccsm questions, whereas power users may want to follow ccsm vs all compiz questions. By that comparison you could make arguments for having all desktop applications be tagged "ubuntu-desktop" (PS: Never ever use this tag, ever.) since you'll need a desktop and Ubuntu to run these applications.
It's not about taxonomy, it's about community :)