Hi @designieplay, thanks for taking the time to post your question and thoughts.
What is a manager?
Management is a different kind of discipline from being an individual contributor. The manager has one single purpose, to make sure a team delivers on its assigned task.
Now that task may be a football match, a track relay, an engineering project or a catering job. It doesn't really matter which form the task takes, what matters is that the team delivers.
Each of the people within the team are responsible for their own actions within the event and may invest much or little effort in trying to achieve it. That does not excuse the manager from the responsibility for the success or failure. Nor should the manager (or at least a good one) try and escape that responsibility.
The managers role is to manage the team before, during and after the event.
Before
They should be looking before hand at each member of their team to understand what their needs are in terms of skills, training and personal needs. They should also be looking to see if those people are team players and working to build the team on a constant basis.
During
During the event they should be looking at how team members are performing and take action to control and guide that for the best result for the team. Even if that means pulling them out if they are not performing well or damaging the team. That applies even if they are the "superstar" in the team.
After
After the event the manager should provide timely feedback and encouragement to make sure that the team knows where they did well and where they went wrong.
Failure is expected
When discussing management it can be easily forgotten that failure does and will happen. Even the most successful companies and teams in the world all fail on a regular basis. Some people are scared of failure and therefore won't enter management as a result.
Conclusion
Going back to your original question, the reason that the manager gets the blame is that they are ultimately in charge. They have control over the team and the individuals. If someone is not playing ball, then the manager needs to fix that situation before it damages the team. They should start with working with that person to understand any issues and resolve them, but if after an appropriate time they don't change their ways, the manager needs to be willing to manage them out of the team.
I hope in someway I have answered your question.
RE: Why do Managers Receive All the Blame When a Team is Underperforming?