That's a fair question, but you'd also need to ask it about essentially the entire history of the labor movement. Why did coal miners fight and die for modern labor laws, rather than finding different work? In the big picture, there are structural forces that get in the way of a simple supply-and-demand view of labor. People's lives are sticky, and the next-best-alternative to a person's current job is often much worse, rather than just a little bit worse.