If the whole union will quit unanimously if they do that, then they have effective monopoly power over labor for the company.

The company will die if they try to bypass the union. In this case they could distort compensation far above what a competitive market would bear, and consumers of Kickstarter eat the cost (e.g. broader society).

It's definitely not a free lunch where workers get paid more and there's no societal cost, as many would like to believe