The population was too high and the institutions were robust. The institutions were also loosely identical to the other entities of the old world, and therefor

The population was too high and the institutions were robust. The institutions were also loosely identical to the other entities of the old world, and therefor designed to survive imperial institutions of similar kind. This is similar to the British occupying any other large population center / former power in the old world. They won't probably be able to wipe the whole culture out.