My understanding has always been that one of the "killer apps" of democracy as a system of government is peaceful transfer of power. It seems like one of those "nobody asks what the old software did well" questions; so many people (i.e. Americans) are so used to the idea of peaceful transfer of power that we don't ever think about what a major achievement it is, and how dependent on it everything we take for granted is.
Another advantage of democracy is a source of popular legitimacy for the government, which helps prevent coups. Dictatorships struggle with this, and have to apply other countermeasures to prevent coups.
Unless a dictator is some kind of super-popular national hero or has managed to convince everyone that they have a divine right to rule, they depend on the support of a group of elites to maintain their power, and have no choice but to prevent other ambitious people from concentrating power themselves. This means that even in cases where the dictator happens to be wise, skillful, and benevolent, their regime will suffer from corruption and fragility, because they have to keep doing favors for their support group to keep them loyal or else risk a coup.
Being a dictator is a position that tends to invite well-grounded paranoia and suspicion, because you know that ambitious and bloodthirsty people want your job. So you need to keep files on people.
They can't defer too much independent authority to talented bureaucrats or military generals or private business leaders, at least not without some guarantees on their loyalty, or else they run the risk of those people attempting to seize power. They can mitigate this by developing a cult of personality, but that makes it impossible to gracefully admit mistakes, and in conflict with maintaining a free press.
And the benefits derived from that. When the consequence for the elites of losing the fight for political power is being targeted personally, imprisoned, or even killed, it makes them cling to power using much more brutal and violent means to avoid this fate, which means more repression for the average folk as well - no dissent can be tolerated. In a modern liberal democracy, they know that they can lose an election cycle without losing their head.
This is why things are so concerning in US - we've already lost this benefit, even though the elections are still genuinely free for now. I don't think they will remain so for long now that the stakes for their losers are so high.
