Virtually all previous European holdings and colonies in Asia and Africa are today governed & almost entirely populated by their pre-colonialist population. Why is this not the case in the Americas, Australia and New Zealand, where the aboriginal populations today are very small and yield very little political power?
Europeans simply didn't emigrate in massive numbers to Africa and Asia like they did to the Americas and Australia. Many of the Europeans who did colonize these places ended up leaving after independance. When decolonization took place, new African and Asian nations were controlled by the natives because they still made up a vast majority of the population, despite their colonial history.
When Australia, New Zealand, and North America gained their independence, Europeans (whites) vastly outnumbered the natives, except in places like Bolivia and northern Canada. The decendants of the European colonists had the political control because they vastly outnumbered the natives.
There was no plague to wipe out the populations of Asia and Africa, and Australian aborigines didn't have a very large population to begin with.
South America (as well as the rest of Latin America) is a different story. The natives and the site colonists ended up interbreeding with each other, and a whole new race (mestizo) ended up taking control.