The answer is obvious: the career line offers an opportunity to involve oneself in public service. There is diversity in the fields one works- be it taxation, social welfare, rural development, corporate affairs and so on. One learns a lot. Great scope for personality development. Enormous source for self-satisfaction. Equally important, if not more, is that working for the country as a civil servant enhances one's selfesteem.
The civil servants implement the policies made by the Political Executive and execute laws and policies to attain the goals of Welfare State which is what India is according to the Constitution. The civil servants in their initial career implement policies even while suggesting minor changes. Later in their careers, they are the virtual authors of the public policy. The best civil servants never retire. Or rather, they are in such demand that they are not free to retire- they find place in Tribunals, advisory bodies like NitiAayog, become advisors and so on. This work profile makes Civil Services irresistible for the best and the brightest.