For large groups, actually, most restaurants do do this. And they usually have it posted on the menu or somewhere so the alert customer will not be surprised. If you make a reservation over the phone they may even tell you then.
Sadly the dine-n-dash mentality would have done this anyway, even without the excuse of an added gratuity.
The Mayor of Richmond Va always does a dine-and-dash. He thinks he shouldn’t have to pay. Restaurants have started slow walking his service or outright refusing to serve him unless someone else is picking up the tab.
IT better be printed in huge letters on the front cover of the menu or is should not count legally. Who reads every fine print in a menu? There is so much of it. Things like “Add a side salad for” “substitute for” When I see it on the front cover then I can say no thanks before ordering. And it people chose to pay it it is still not a tip because it did not ensure anything. It is not based on the quality of service.