Some of it is deserved BTW; some big unions were/are corrupted and some were connected with organized crime. Even more innocently, unions have been quite conservative; as jobs and technology changed some were very resistant and fought modernization (requiring people who were not needed to be around). But a lot of it also stems from corporate resistance to unionization and the high regard in which ordinary people hold the opinions of corporate managers in the USA.
All that being said, unions have been very good for labor, and when I've worked in union shops (not in a unionized role) they've been really great in terms of qualified people and high quality work. I built my house using union labor and I'm glad I did.
Europe is not immune to these diseases by the way. Certain French unions certainly negotiate against the greater interests of society. And in Germany my non-unionized brother in law (a mechanical engineer) was not allowed to work late at VW -- he was trying to finish a project one evening and a union guy came by and cut his PC's power cable while he was designing a part.