What do you mean that it's "much easier to just pay people a decent wage"? Do you mean that it's much easier to convince companies to pay their employees more than they have to, or that it's much easier to pass higher minimum wage laws?

Neither of these seem easier than "convince the public to toss in a few extra dollars when they use a lowly paid service".

I see "make sure that all working people are paid fairly" as a very difficult problem, and tipping as a moderately effective hack that's easier to implement than the cleaner fix of higher minimum wage of basic income.