Why Coaxial Cables are Highly Insulated?
Coaxial cables are highly insulated in order to prevent leakage of signals and prevent signals from the surrounding from penetrating to the inside of the cables.
The cable do not only prevent leakage of signals but also electrical energy seeing that the materials used in insulating the cables are Non-conductors of heat and electricity¹.
The advantage of coaxial design is that electric and magnetic fields are confined to the dielectric with little leakage outside the shield.
Due to the level of insulation in the cables which prevents outside electromagnetic fields and radiations from penetrating into it, interference is avoided.