> you should just consider a 15% tip a part of bill for anything where you sit down and have food brought to you
It's not that simple. I fully agree that in cases where the establishment is allowed to under-pay, it's our job to tip. But I've lived in the United States all my life, and there are still enough edge cases in the restaurant industry alone to be terribly confusing. That doesn't even get into questions of barkeeps, hotel staff, taxi drivers, and whoever else.
What if I order at the counter, then I sit down and someone brings me the food? Are the employees who bring me that food making less than minimum wage? How do I know one way or the other?
Even more confusingly, order-at-the-counter restaurants have started asking for 15% tips at checkout. I'm relatively confident that they're not building tips into the wage structure, but how can I be sure?
It's definitely not the fault of the workers that this system exists, but it's a horrible, opaque, and confusing way to do business. At a minimum, restaurants should be required to make it explicit when their employees need the tip.