Lighting diverter strips provide a path of relatively less resistance than the radome, to allow lightning strikes and severe static discharge to make it's way to the airframe where the charge can be dissipated to the atmosphere properly and slowly through the static discharge devices. (Static wicks etc.)
The strips are "consumable". They are eaten away by large discharges and need to be inspected and replaced occasionally.
Radomes are made from non-metal composite materials or from re-enforced fibreglass type compounds. The radome is usually coated with a conductive compound so that it can handle most static charges and pass them to the airframe, but it can obviously not be covered in a metal shroud. The lightning diverters offer an additional level of protection.
Typical damage caused by static discharge on unprotected radomes range from tiny carbon filled pinholes to large holes burned through. Even small pin holes can cause water ingress and subsequent delamination caused by water expansion due to freezing.