You're making a correlation that the best leaders are at the top, but that's not the case. Furthermore, you don't need to be an exceptional leader to know that you need to care for your subordinates.
Yes, there are terrible leaders in the military. There are leaders who go through courses specifically geared for command positions, learn tools on good leadership, and then actively use techniques counter to the learned approach. However, there are terrible leaders everywhere, at all levels of command.
Very rarely are civilian leaders given dedicated time and instruction within their profession on how to manage their subordinates effectively, outside of say academia (e.g.: business school). The military has professional military education (PME) built into all levels of leadership from first line supervisors up to executive leadership (general officers)---The differences between military and civilian leadership is very apparent. Military veterans are often the most preferred candidates, all things being equal, in recruiting pools because of their leadership and performance.