Despite Symbolica being licensed, its source code is still available which clearly shows the author's intent.
It may be important in various contexts, e.g. security or satisfying certain grant requirements in academia, or whenever custom minor modifications are necessary.
cynically, one possibility is the intent to be able to sue open-source cas authors and distributors who had access to it and then wrote substantially similar code. charitably, it's intended to allow users to resolve whatever problems they have with the system, by debugging and, if necessary, patching it
