Depending on where you are in the country, the minimum wage can be as low as $7.25/hr. For tipped employees, that minimum becomes $2.13, with the intent that tips make up the rest.
So, that's a $5.12 difference, with a standard 15% tip a server gets that waiting on a single table with a $40 about in a hour.
Needless to say, most wait staff here are relying on tips for the bulk of their income, and when you fail to tip it's equivalent to making them work for free. I wish it wasn't like that here. But in case you haven't noticed, we have a lot worse problems right now. I don't think fixing it will be on any politicians radar....