This is on one side for tax avoidance reasons. But on the other side everyone I know working in gastronomy rages about Americans and their aggressive credit card usage, how slow usually the process is (these people are trained with cash, plus nearly anywhere in Europe you round the sum to something easy to give out anyway as a tip).

From what I can tell these people simply prefer cash. I just asked and my gf said it's just a lot faster to do it by hand.