Employers are obliged to ensure that employees they are paying below minimum wage because the employee gets tips get paid at least minimum wage including tips.
If an employee lets their employer know they did not earn enough tips to meet minimum wage, then the employer must pay them more to ensure they get minimum wage.
Also, in many jurisdictions of the US where the same minimum wage applies to traditionally tipped employees, the tipping dynamic has remained. For example in California, Oregon, and Washington, the cultural expectation is that customers will still tip waiters, even though the waiters are earning the same minimum wage as everyone else.
If an employee lets their employer know they did not earn enough tips to meet minimum wage, then the employer must pay them more to ensure they get minimum wage.
Also, in many jurisdictions of the US where the same minimum wage applies to traditionally tipped employees, the tipping dynamic has remained. For example in California, Oregon, and Washington, the cultural expectation is that customers will still tip waiters, even though the waiters are earning the same minimum wage as everyone else.