Why do the professionals advise athletes to eat more protein?

What does protein do that athletes especially need?Why do the professionals advise athletes to eat more protein?
Protein is the building block of muscles. Protein is also involved in a variety of body functions. The more active you are, the more protein you need just to maintain the muscles you use.Why do the professionals advise athletes to eat more protein?
Protein helps build and repair muscle. Some sports (like swimming and track) wear the muscle down during hard training and protein helps repair it. Protein also builds muscle and makes the muscle thats already there stronger.
It gives them energy.