I don't see why costs for supplies should decrease, necessarily, even in real terms. I guess you can have consistent churn at a brick & mortar business to keep paying minimum wage by replacing people with younger people as they leave.

But that setup only applies if you're paying at the bottom of the scale and not giving out benefits. Bennies have been increasing by much more than inflation, and the type of jobs giving bennies typically expect a 4% raise, minimum, if you're doing acceptably at it.

A McDonald's franchise looks a steady state because that's the entire point. McDonalds is basically a holding company with a portfolio of some of the most valuable real estate in the world that uses the burger flipping as a way to constantly grow. However, no McDonalds franchise is a steady state unless its in a tiny town immune to inflation where no one wants to open a competitor (and there's very few of those). If a restaurant's profit falls behind inflation it's no longer as valuable a holding in their portfolio.