I'm using the term "structural" here without any clear definition, to be honest. By it I mean that it's about the structure of society, the relationships that are in place, the difficulty of setting up a new school, the resistance of the AMA to open up more residency spots, etc. Points in the process where there's high friction for changing the system to a better "structure", whether or not the change requires financial incentives.
But I don't know if that meaning is shared by anyone else in the world! Thanks for asking for clarification, I'm interested in how you'd communicate that idea.
If there is a shortage of something, I would expect these trade companies to backfill with apprentices who will then grow into their roles.
If there's too high a risk that someone won't be worth the investment, then that seems entirely financial to me.