One bartender I talked to made the (astute) observation that people feel more generosity toward individuals than to restaurants -- it de-personalized the transaction from the customer perspective, which turned the service charge into a food tax.
In other words, someone's being dishonest.
In most cases, still, the model I seem to see (and I live in the PNW) was a 15/18/20 tip model, and for personal services (nails, hair, etc.) 25.
Food servers would have us believe that poor tipping and other practices have them one shift away from being homeless, or "I have to pay the IRS to serve you, because they assume I'm getting tips I'm not"...
... and yet, when a 20% "tip"/surcharge (which would be on the high end, I feel, most of the time) is added on to every order...
"This sucks, we're making less money".