Because in many cases they can be. Really depends on your industry, and the Union you're in. Some are the only way the job is tolerable, sometimes they hold workers back, many times unintentionally but still happens. I'm in trucking, for us, we're WAY better off with Unions behind us because trucking has VERY outdated regulations and many employers exploit that likes it's tax code loopholes.

I'm in a right to work state, so people don't have to join the Union if they don't want to, you'd be amazed at how many don't! Many of the ones who don't are the people in the boomer years who have years of gripes against the Unions, people that spends decades as union workers. I've heard a lot of shit, it's not all bullshit. There's +/-. Only ignorant people claim otherwise.