Poor management

Can anyone answer how a manager can be at least 2 or more hours late on a daily basis and still keep their job? I recently missed a few days because I needed surgery on my foot to clean out an infection, I'm just crew, but was put on a final because I failed to cover my shifts, I was told It is my responsibility to cover my shifts, not the managers. Keep in mind I had a doctor's excuse from the er covering every shift I missed.