Why would you cover for someone who wasn't doing their job? Unions don't make it impossible to fire a bad employee, they just require normal things like documen

Why would you cover for someone who wasn't doing their job? Unions don't make it impossible to fire a bad employee, they just require normal things like documentation and giving the employee a chance to improve. If I started doing someone else's work making it impossible for the bad employee's boss to know there was a problem that's not really a issue with unions.