It is a “service charge” and is included in the overall price of the meal and is how the business pays the server.
It must remain voluntary.
Exceptional servers do exceptionally well.
Good servers do alright.
Poor servers look for a job more appropriate to their skill set.
The customer wins.
If everyone gets the same “tip” via a service charge on the bill, there’s no added incentive for “exceptional service.” Service will be “acceptable,” in other words somewhere between “ok” and “mediocre.”
The customer suffers and the business suffers.
The way you describe it IS the way it used to be. Not now...... at least not at many restaurants.