You go to a bar and get a glass of water from the bartender because you are driving. You don't pay for it and you don't have to tip. The bartender is doing all the same work as a pour of Jack on the rocks.

Sometimes it is just how the system works. A lot of things work like this in life. It is fair to question it but people do build their livelihood off of it at the same time.

No one has to follow the rules but your driver or server is more likely to do a better job and a quicker job if they think they will be getting paid more.

The bartender is not going to ignore their high-paying guests to get you the water but they will eventually get it. They get their base pay (hourly wage) for doing this.