Tip money is black. It's tax evasion. As such, it doesn't produce return services from the fundamental service provider, the Government (national security, law and order, infrastructure, education, health and social insurance).
Tips cannot motivate, on the whole, a badly paid, uninsured workforce.
A tip-based economy is also unethical, IMO.
When I want to buy anything, including services, I want to deal with the vendor. If the vendor says "it's almost free, but you 'll have to bribe my slave into doing the job", it's a deal breaker for me. Why not whip the slave, to provide some motivation, if we take that path?