So people who are vegan drink protein shakes?

Not all of them!: That is a vast generalization. Certainly some vegans drink protein shakes but many don't. There are plentiful sources of protein in a vegan diet- nuts, seeds & beans are the best sources, but even foods like kale, broccoli, avocados, potatoes & quinoa contain surprising amounts of protein, it's really not that difficult to get plenty of protein on a vegan diet!