Lieutenant colonels are the equivalent of corporate senior directors (O5). This means they could be either a battalion commander, approximate footprint of 300-500 people, or a senior staff officer for a command/division. By that point they are expected to have at least 15 years military experience.
The challenge at that level of management is writing and evaluating plans for their organization that must be able to move across the battlefield and roll up all corresponding metrics. Think of that as moving your entire office staff to a new location 50 miles away as frequently as needed. A 6 week bootcamp won’t get you that. As someone with 28 years military experience and a corporate nerd with almost 20 years experience I promise that corporate management is not the same. That part time job can suddenly feel like a full time responsibility.
The exception to this are licensed doctors and lawyers. They enter the military as captains instead of lieutenants.
And chaplains, I think. The three professions corresponding to higher faculties in a medieval university. Many weird things in the military make more sense when you recognize them as leftovers from ancient social structures.