They weren't talking about general contractors, but trade-specific contractors with multiple tradesmen working together. A crew can supervise and train newer m

They weren't talking about general contractors, but trade-specific contractors with multiple tradesmen working together. A crew can supervise and train newer members, and the more senior tradesmen can make sure the output of the entire crew is high quality even though some of them have a lot to learn. Even for the explicit goal of getting juniors trained, the crew that does the better job is probably doing more training than the worse crew.