That may be true, but I suspect that it’s also hard to compare apples to apples. A burger in 1959 is hard to compare to a burger today. Today’s burger almost certainly has twice as much meat. The invention of (and ubiquitous advertising of) the quarter–pounder means that everyone had to make their burgers larger to match. Sides are larger, drinks are larger, etc, etc.

But labor costs certainly have gone up too.