>The other reason being it involves a degree of social pressure and shame, if one doesn’t tip enough.
It's standard to tip 15% for decent service in a restaurant(sans win). You are of course free to tip more for good service or less for crappy service, but unless your experience is truly exceptional (in either a good or bad way) you can never go wrong with 15%. This is standard any US restaurant where you sit down and are served by a waiter or waitress. You are never "forced to tip", but you will be universally looked down upon in any sit-down establishment that you fail to tip in, so you might be best off not returning.
The last metric in this 2017 study, before the pandemic, showed tipping was between 18% and 19% in, "surveys (that) are aimed at diners who patronize full-service midscale and upscale restaurants". It also shows a downward trend in the last few data points. All things considered, including diners who patronize "downscale" full-service restaurants (like diners), and given the many decades-long standard of 15% tips, it seems to me a safe standard to continue to use. Certainly no foreign visitor will ever face vitriol for tipping 15%.
The 15% standard supplanted the previous 10% standard somewhere in the 1970s and lasted to the early/mid-aughts depending on where in the US one lived. I don't agree that ~30 years is "many decades-long". Further, that 15% itself was an uptick from the prior standard demonstrates that we're dealing with a moving target, for better or worse.
It's standard to tip 15% for decent service in a restaurant(sans win). You are of course free to tip more for good service or less for crappy service, but unless your experience is truly exceptional (in either a good or bad way) you can never go wrong with 15%. This is standard any US restaurant where you sit down and are served by a waiter or waitress. You are never "forced to tip", but you will be universally looked down upon in any sit-down establishment that you fail to tip in, so you might be best off not returning.