The time to get as many students in as they can. Some schools do double casts if they have enough demand.

My son is a terrible actor but he was “in” every play. His part was lucky to have any lines but they always got him in. He developed a group of friends. He got a lot of confidence from being on stage. He had to work hard to learn to sing even a little. He spent hours trying to get his dance steps down. You might have to work harder when you lack natural talent. He benefitted from participation and he didn’t need to be the lead.

Sports have similar benefits for participants, everyone else in education would be focused on maximizing the number of kids who can benefit from that.