If your serpentine belt keeps fraying, there are a few possible reasons. First, the belts are made of rubber and over time, they can dry out and crack. This is especially true if the belts are exposed to excessive heat or cold. Second, the tension on the belt may not be set correctly. If the tension is too loose, the belt will slip and fray. Third, the pulleys that the belt runs over may be misaligned or damaged. This can cause the belt to rub against them and wear down. Finally, there could be something caught in between the pulleys and causing friction. Whatever the reason, if your serpentine belt keeps fraying, it's important to have it checked out by a mechanic to avoid further damage.