Strong family connections.
My wife has played principal boy in several (she had unbelievable legs) and my son was as a sensation as Sunblest, the very camp son of the Widow Twankey! His throwaway line of "Oh, very bijou" on coming on stage for the first time, originally an ad lib but left in at the director's insistence brought the house down each night!
As you say, it's a British thing, but happy memories.
Waiting at the stage door as a nine year old to worship at the feet of an eight year old chorus girl. The stuff of childhood!