I've lived in 5 different states over the course of my life. The operating environment varies substantially. Local ordinances vary greatly. Fuel costs. Climate (vehicles in Phoenix are not exposed to rust, salt, etc while here in Michigan they are). Local labor laws, unemployment costs, insurance costs and restrictions. It's literally completely different in every state.
Businesses love to subcontract, particularly when it is outside their core competency. It's a line item on the expenses.
If unions did not exist I would posit that they would still operate this way.
Yes, I think so. Furthermore, if unions were mandatory and universal, businesses would still favor subcontracting when paying for work outside their core competency.
By which I mean, their superior quality of delivery is the reason I buy stuff from them.
The worst Amazon driver is better in every way than the best Fedex or UPS, and I'm loathe to dignify Canada Post by even mentioning them.