I am sure Applebee’s menus show that the 18% tip is added for parties over X. It’s done that way at almost all US restaurants.
In Europe the automatic tip (15% IIRC) is on every bill. A guest can then leave a gratuity if they choose. That causes problems when Europeans first eat at US restaurants and assume the tip was included in their bill. It works more favorably for European waiters.
The restaurant industry and the hospitality industry generally operate at incredibly tight profit margins vs most businesses. It’s one reason so many restaurants go out of business in short order (so to speak).
If a restaurant schedules, say, 10 waiters for a shift at the higher hourly wage, but has only enough customers to fill 5 tables, they’d lose money on that shift, and soon be out of business. If they understaff for a shift, customers get poor service and won’t return. As it is the waiters share the risk against their own ‘profit’ in the form of tips.