If you actually look at the commits, it's mostly fixing the build and tweaking it to work on modern platforms. My personal opinion after trying it, I would not suggest use of Motif or CDE for anything besides nostalgia, it has some serious usability issues. But if you enjoy it, more power to you.
Who cares about CDE, the classical UNIX desktop, as in the way that BSDs and GNU/Linux keep pushing for the old days with their fragmented stacks.
macOS, although a UNIX, follows the same ideolagy as NeXTSTEP, where UNIX compatibility was a means to bring software into the platform, and that was about it, GUI software was to be fully taken advantage of Objective-C Frameworks.
Yes. "CDE" itself stands for "Common Desktop Environment". (Wikipedia says it was "part of the part of the UNIX 98 Workstation Product Standard", and if you remember the 1990's like I do, it was, indeed, supposed to be the "standard" desktop for Unixes.)
CDE? That hasn't existed for decades.