> If a company doesn't want to meet the union's expectations for the wages and benefits of their members, it can simply fire all the union members or wait for them to strike and hire their replacements.

Not agreeing with OP, but you generally can’t fire striking workers. Replacements are difficult as you still owe the striking workers their positions if they return.

Lots of caveats to all of that, but it’s definitely not simple. If it were there would be very few private unions.