In the US tipping isn’t just a cultural expectation. There are fundamental legal differences between tipped and non-tipped employees. For example, federal minimum wages for tipped employees are close to $2 vs the $7 for non tipped employees.
On top of this, in the US tipping has a history that has roots in post-slavery racism.
In a country with race-based segregation, it's very convenient mechanism to have a method of compensation that can be altered based on your physical appearance.
