Usually (internal) damage, caused by wind, rain, ice, etc. Could also be a manufacturing flaw. The damaged section will have a higher electrical resistance tha

Usually (internal) damage, caused by wind, rain, ice, etc. Could also be a manufacturing flaw. The damaged section will have a higher electrical resistance than what it was designed for, and as a result that section will dissipate more energy (heat). The splice/patch effectively increases the cross sectional area, which will lower the resistance, which will lower the dissipated energy, which will lower the heat.