I don't think triboelectirc effect is the main problem, I think its the stuffing. Those cables are made of a type of foam insulation quite often, which gives it the flexibility required. However, getting this foam to be stable is hard, to ignore bending , and so forth. You won't find a VNA cable better then a standard piece of coaxial hardline, but the hardline gives you 1 bend, whereas the VNA cable gives you many more.
They are typically made with solder, the braid is soldered and the center pin is soldered. They might make extra effort to get wire that is drawn to a better specification, tighter temperature control on the insulation process, tighter purity control on the reagents used for creating the materials as well.
I imagine its somewhat like a good cappuccino or swiss cheese, good control of the bubble foam