That's a fallacy. There are certainly some unqualified elected leaders, but humans living in democratic societies have yet to shake the mental framework we've constructed from centuries without self-rule. We invest way more authority into a single executive than they actually have, and blame them for everything that goes wrong despite the fact that modern democracies are hugely complex systems in which authority is distributed across numerous people. When the government fails to meet people's needs, they lack the capacity to point at a particular Senator or a small party in a ruling coalition and blame them. It's always the executive.
Of course, the result is that people get fed up and decide that the problem has been not that democratic societies are hard to govern by design (they have to reflect the disparate desires of countless people) but that the executive was too weak. They get behind whatever candidate is charismatic enough to convince them that they will govern the way the people already thought the previous executives were governing, just badly. The result is an incompetent tyrant.