You mean like Apple does with it's silicone-rubber cables that resist cracking...
You forgot to include the obligatory "/s". The rubber shielding on Apple's power cables is anything but crack-resistant.
(Not that I'm suggesting Microsoft's choices don't suck, but don't hold up Apple as an example to aspire to in this instance.)
I think the design goal was to look and feel expensive and trendy. How it wears is a different discussion.
No, the Design Goal was to provide increased flexibility over the typical PVC-jacketed cables, under more environmental conditions (particularly cold).
It was likely inspired by the cables on the soldering stations in the engineering labs at Apple. The base-to-pen cable is often silicone rubber-jacketed, and in my personal experience, they are unusually flexible and supple, tend not to kink nor tangle, and stay that way over time. The exact same characteristics that are exhibited by my MacBook Pro's silicone-rubber (or EDPM)-jacketed AC adapter cables.