Teflon insulation sometimes ages badly, tending to crack into "macaroni" segments on the conductors. I don't know what causes it, or if it happens to all PTFE-insulated wire at some point, or just certain processes/etc.
I used to have some cockpit panels from an old 737, and all of the wiring still attached to them was like this at some point in the harnesses (it might be why they were removed--easier to replace as a whole than rewire in place).
I've also seen the same thing in various old hubmotors that used teflon-insulated wire.
Same thing in some old server racks wired up that way.
How long it takes to get this way varies depending on the properties of the teflon itself, the environment it was in, and the physical stresses it underwent over time, but I've seen stuff as young as a few years in hubmotors that failed this way. The 737 panels were probably at least 30-40 years old when I first saw them (already failed insulation).
Another issue with PTFE is it is "soft", and flows under tension or pressure, so that if you have a wire resting on or pushed on by something, the insulation tends to flow away from the conductor, allowing a short to whatever is pushing the insulation away.