Toyota has no set schedule for replacing belts. On your car it is supposed to be inspected every 15000 miles and replaced if it show cracking or fraying. Some mechanics consider periodic replacement a good service to their customers because if it breaks you lose power steering and the alternator. On your car you have no steering pump but with the alternator not working, the electric power steering will stop working pretty quick.
I don’t proactively replace serpentine belts if they look good, I have had them last the life of the car as long as it was a car with a timing chain. If a timing belt, I change them together because the serpentine belt is already off.