Finally, I figured out how to expess why their complaints bother me so badly.
If you want someone to do more then you need to pay them more.
But who do you think is busier? A McDonald's worker 40yrs ago or today after 40yrs of cost-cutting optimizations. Because a big part of those “optimizations” has been maximizing the output of each worker by firing the rest.
Despite this, real wages are lower than then. It is unfair of the wage setter to expect more results for less incentive, and when customers don't blame the right party, they encourage the injustice to continue.