It is the way that server pay is structured here. There are some sad historic roots for the practice but the simple fact is that servers do not want to transition away from tipping. They are better off with the current system.

For diners, it is very very simple. When you are served, you tip. The going rate is 20% for acceptable service. It is very simple to calculate and you know before you even choose a restaurant that you will be tipping. It's just not hard.

And of course people who fail to tip properly are scrutinized. That is tantamount to running out on the check. If you don't tip well, you should be criticized.