Historically, democracy was rarely favored by philosophers: Aristotle classified democracy as a deviant constitution because it gives advantage to the rich populists. Plato claimed that democracy is dangerous due to its excessive freedom. Churchill famously said, "Democracy is the worst form of government, except for all those other forms." Some people are scared by the idea of the mob taking power with unpredictable consequences (this is called demophobia or ochlophobia).
So, why is democracy taking over the world? Even autocratic states are now claiming to be democracies and attempting to mimic its institutions. The key lies in the dispersal of power, or the diversification of power.
Democracy, unlike all other forms of government, provides a mechanism for spreading power, which makes it "fault-tolerant." Similar to how genetic diversity in biology allows species to tolerate environmental changes, power diversity makes democracies resilient to stresses such as coup attempts or pandemic outbreaks.
This is why democracy has so many forms and variations, and why it tends to remain in place once established (with rare exceptions, such as the Roman or Galactic Empires).
In proper modern democracies (suffrage was very, very limited in ancient republics to the point they were more like what people think when you say oligarchy), there's also an actual incentive for politicians to address the greater good. Kings and dictators only do so when they feel like it.
This happens mostly with either newly elected officials, when the imposter syndrome is still strong, or with officials who want to be reelected, and have a strong opposition.