AFAIU, "can't start with C" was not an afterthought. It was explicitly meant to be the anti-CDE, something better to prevent the clunky and non-free CDE from becoming the default DE on Linux.

(I actually somewhat like the look of Motif, CDE's toolkit. It is maybe the association with reliable, expensive, professional (etc) Unix application software. While proprietary, still much cooler than Windows.)