I think it's more than just increasing the odds, but also the severity.A bit of a myth that rodents only chew soy based wiring. Sure, soy will increase odds.
Chewed wiring + nesting material = recipe for disaster in an engine compartment. Lots of secondary things that can burn hot.
I strongly suspect that a rodent biting into PVC insulation will take one bite, decide it's not food or useable nesting material, and turn around. But when they bite into and realize it's food, they pull up a chair and a few friends for the feast.