These guys are adults and can make their own decisions (like no thigh pads). Just like when I am on a bike path enjoying a morning ride along the beach, I don't wear a helmet.
It isn't easy to bark out calls with a mouth piece. But if he got rocked, like running backs and line backers do every play, he'd put one in, for sure.
The ringing in the head after your teeth slam together is brutal. He's an adult, he'll make a decision what is best for him.
Sorry disappoint all you socialists/communists who want to control people's every waking moment.