Most of the problems with US unions can be traced back to anti-union legislation that used the promises of entrenching current unions as a carrot to get the law

Most of the problems with US unions can be traced back to anti-union legislation that used the promises of entrenching current unions as a carrot to get the laws passed to suppress new unions. New unions are much harder to create today, even more so if there is an existing union that covers similiar employees to your own. And old established unions are hard to get rid of even if the majority of employees are unhappy with it and would rather it was either gone or replaced with a different union with different rules and leaders. And an old entrenched bureaucratic political position is an easy target for corruption.