I think a lot of it is sheer idiocy. The elders don't stop and use their brains when assigning parts.
My one sister was eleven or twelve when she was assigned a talk about how to have a successful marriage. Mom was PISSED and didn't keep quiet about it. She told an elder it was inappropriate for them to make a young unmarried girl lecture an adult woman on a subject she had no clue about. Mom ended up giving the talk herself, which was ironic given she was divorced after an unhappy marriage.