Why is that sentiment (general sentiment, not just yours) different in case of restaurants? When I meet Americans and when I leave w/o tipping, which is not co

Why is that sentiment (general sentiment, not just yours) different in case of restaurants? When I meet Americans and when I leave w/o tipping, which is not common but normal where I live, they feel really offended and sometimes, I suspect, they might have thought they have to hangout with stingy persons like me. I am not sure whether I am meeting a very different kind of Americans or it's ingrained in the culture there in US. Problem is they are usually not even willing to see that it's a different culture here, or that we tip based on the service and/or the fact whether the restaurant charges a "service charge" or not (it's additional to service tax).