First line managers rarely have the power to simply fire on a whim. There has to be cause, and it needs to be evidenced, and there will be multiple people involved in the decision.
If you're a more senior engineer, you may report to a manager of managers, and line managers may be your peers organisationally, and probably not paid as well as you are.
Engineers also get to make a different kind of decision to managers; and it's often the longer term, higher leverage, more strategic kind of decision. Line managers are much more operationally focused and rarely have the bandwidth or tasking for strategic decisions.
First line managers rarely have the power to simply fire on a whim. There has to be cause, and it needs to be evidenced, and there will be multiple people involved in the decision.
If you're a more senior engineer, you may report to a manager of managers, and line managers may be your peers organisationally, and probably not paid as well as you are.
Engineers also get to make a different kind of decision to managers; and it's often the longer term, higher leverage, more strategic kind of decision. Line managers are much more operationally focused and rarely have the bandwidth or tasking for strategic decisions.