Expediency; because if we take that line of argument to its logical conclusion the ownership of most of North and South America and even Australia ought to be reverted to the Natives with all those of European stock being asked to pack up their bags and leave for the shores of their forefathers. But we don't do that; because we recognize the impracticality of it all.
For quite the same reason most other developing countries are or were in an equally bad shape - Governance !
One does need to conduct an anthropological deconstruction of any country to figure out why its failing on most social and economic indicators. Even the present fanaticism is a failure of Governance because if you bring about an anthropological reconstruction of a society for the worse to serve strategic and political objectives you can hardly cry foul if the experiment doesn't work out and blows back in your face.
We are guilty of all the things that fall under the singular category of 'Bad Governance' !
Not entirely, it depends on whether the species introduced did justice to the resources they found. In the case of many countries, they did.. in our case.. they did not. Taking the easy way out of blaming the government or leadership or fate is only indicative of how utterly lost we our to a doomed fate; not realized that the ultimate fault lies in each one of us and the wilful ignorance of it only makes the very idea of a nation state based on us laughable.