I remember when I spent time in the US, tipping was the absolute worst part of the experience.
If I was with a big group going to a restaurant we would have a server constantly checking in with us, chatting and telling stories, getting us deals and freebies. When I would go out alone I would get ignored. If I dressed down I would be treated worse than if I was dressed up. One time I even waited an hour for a table before walking out as larger groups got seated ahead of me. How people are treated is based on how much money they think you'll hand over.
Everything about tipping is greed and it's gross.