But why did Rome have a system that yielded bad leaders? Part of it is just the nature of autocracy, part is a lack of effective succession planning in the Empi

But why did Rome have a system that yielded bad leaders? Part of it is just the nature of autocracy, part is a lack of effective succession planning in the Empire, part is a return in the late empire to powerful generals with effectively private armies, part is a similar return to what amounted to proscription so entire generations of potential leaders were killed after each civil war. I don’t think you can point at one proximate cause over any others without asking why Rome was vulnerable to that thing particularly.