At least that way, I know my server won't starve. And a tip becomes just that - a tip, a gratuity for superb service. Diners frequent restaurants for the service. If we just wanted food, we could buy it cheaper at the grocery store. Instead, we pay inflated prices for someone to take our order, cook our food, bring it out, clean up after us and obey our commands.
Food servers tend to be women who are unskilled or uneducated.
They perform grimy, subservient, back-aching labor we take for granted. If some local restaurants pay their waitstaff living wages, I'd like to know. My dining experience would be enhanced knowing my waitress also can afford to eat tonight.