There are many examples of effective governments, yet it still is considered an outstanding achievement.

It seems correlated to the "size" (population and density) of the nation? Neglecting nations in a fast-paced social/political transition, most effective governments are active in "small" nations (including politically decentralized ones).

I assume this is a snark, more than 300 mayors to govern 1 city the size of New York doesn't seem like an effective government to me.

Is the correct effectiveness metric the number of people involved or the outcomes for the people served by that government? I don't really care how big/small our government is if everyone is experiencing a high quality of life.