" It's something you only care about when it's broken." - you do realize that plumbers are needed for new construction and renovation? Actually, given the needed improvements in infrastructure and new building projects, a lot of skilled labor is needed. I am really not seeing robot electricians, plumbers, etc. for many decades to come.
I am really unclear what you think unskilled labor is.
I really don't think the labor stats match your belief in regard to the skilled labor, and I the unskilled positions your are mentioning are being limited more by raises in minimum wage / economic conditions versus automation / demand.
I am really unclear what you think unskilled labor is.