As a director, you may think you know the talents of the students who will take part in your groups, but you don't always know for sure. Then again, you may be surprised at new talents or sudden development of latent talents as they appear in the students. This situation is what can cause ulcers, for sure.
Number 1 - They have done it before, so it is a known quantity. They may already own a lot of the costumes, props and scenery, too.
Number 2 - The lead parts are few, so the acting/staging/rehearsing is simplified. The Ensemble can absorb any and all other students that only have to be taught the songs to sing plus a few dance numbers.
Number 3 - Many schools or children's theater companies have very limited budgets, so they must compromise on acquiring new or expensive materials, or hiring extra helpers.
My hope is that some brave directors/teachers will take a look at other options as they plan their new seasons. It is good to choose vehicles that can give more than just a few students featured roles and keep more kids busy with meaningful parts throughout the entire show. Take a chance on new works that may be a challenge, but are so worthwhile.
"The Adventures of Dick Whittington" - interesting historic setting, old English Pantomime characters, fun music and dancing
"Never Cry Wolf" - Aesop fable, ancient Greek setting, story within a story, music from many styles
"Parazade's Quest" - Tale from the 1001 Arabian Nights, opportunities for five female leads and as many males, action, drama, and suspense
"The Tale of Chicken Licken" - Comedic parts for many characters, easily separated into rehearsal units, irresistible costume opportunities
"The Frog Prince" - familiar story without the love interest, parts for many princesses, and plenty of comedy and action for the Knights
"Momotaro" - a beautiful retelling of a Japanese folktale using Kabuki theater stylizations, colorful costume and dance opportunities