If truckers or dockworkers go on strike there's no food on the shelves, if coal miners go on strike the lights go out, and so on.

As a consequence of this, employers are motivated to make a deal not just by missed opportunities to make money, but also by politicians, other powerful capitalists, and public opinion.

Of course there are plenty of unions where this isn't the case; theatres and hollywood are unionised despite the fact nobody freezes or starves when they go on strike.

Game developers are, I think, closer to the hollywood position than the dockworkers position.