Small point: According to Indeed, the (average?) salary for a machinist at Boeing is $87k, so it'd be more like $40-45 an hour these days.
It's relative
To what? Working at McDonald’s?
Relative to what other jobs in the area pay and the cost of living, of course. The competition may in fact be McDonald's paying $12 an hour or Walmart paying $14.
It's extremely easy to clear more than 25-30 an hour waiting tables in a lot of places.
The places where you can easily clear more than $25-30 an hour as a waiter are also places with high cost of living and expensive housing. As a counterexample, in my area (a midsize city in a low cost-of-living state), restaurants universally suffered from sharp labor shortages last year. $25-30 an hour would let you live comfortably here, meaning they should have had a lot of applicants; therefore the money just wasn't there.
My wife was a waitress for years (but not in the last decade or so). A four hour shift at Sizzler (yes, the stake house that everyone loves to hate) would get her about $25/hr on average easily. A decade ago. In a small town in the Inland Empire of SoCal, amongst the lowest cost of living in California.