The investor class has convinced many tipped workers that they will make less money if they receive a living wage. People dream of that big Saturday night rush where they go home with $1,000 in cash, while forgetting the far more common experience of struggling to pay bills because some cheapskate stiffed you on your only big table for the night.
Don't forget that workers like tips because tips allow you to cheat on your taxes. I've never met anybody who worked in a tipped job who reported 100% of the tips they received.
Another issue is that everybody thinks they're above average. Waiters / waitresses think that if there are no more tips, they (being above average) will lose out.
Hmm, what if instead of removing taxes from tips they make the tax rate on tips 100%? It would effectively eliminate tips as a source of income forcing companies to pay competitive wages without factoring tips in. Also if people knew 100% of their tips were going to the government they'd stop tipping pretty much overnight.