Human Nature

[Ivan Denisovich]

These politicians weren't chosen in elections.

Of course not, in most cases. But they are tolerated even in the absence of elections, until a polity decides that "this is bullshit". I saw that exact thing happen in Iran in 1978, where an autocrat who was happy to kills thousands to preserve his power was all the same chucked out of office.

No government can survive when the body politic is fed up. Louis XVI, Tsar, Shah, the Soviet Union, all terrible regimes, all overthrown either by the people themselves or by a military that responded to public opinion.

If I recall correctly it was food that played big role in overthrowing Louis XVI and Tsar. It would indicate that people are willing to tolerate much as long as they're fed. Other than that I imagine populace reason for not standing up to tyranny are as varied as populaces itself.