relic of slavery
... what?
Tipping was something that the patricians/bourgie upper class did to help uplift the waiters/service staff in Europe. It caught on in the USA in the late 1800s and fell out of favor from that upper class in Europe by then.
Largely, USA coopted a "noble gesture" from wealthy Europeans and it has persisted ever since for like a century.
Anyways, I hate tipping as well.