Because during bad times the ones that make bad decisions don't survive or at very least are removed from positions of power.
It's more common for bad leaders to make the bad decisions that cause the bad times, and then either be deposed by violence or cling to power with violence, making everything worse. See Stalin, Mao, and also the entire history of sub-Saharan Africa after colonialism.
I'm certainly not a fan of American electoral democracy, but one can say that at least it's mostly peaceful and allows in theory the people to make a choice between qualified and vetted candidates. In "hard times" the mechanisms created by civil society to select competent leaders tend to break down. So rather than removing bad leaders from power in hard times, it becomes even harder to remove such leaders, and even harder to determine whether a leader is good or bad until after he's in charge of the army's salary.