It sounds like all nigerians want to work for an oil company WHY?

Don't make generalizations. Not "all" Nigerians want to work for oil companies. But I do see where you are coming from.

The short answer is Money. The long answer? Money.

Honestly, with the way things are, maximizing your earning potential only makes sense. If you go to school, pay the same, and put in roughly the same amount of effort as students in other majors, why won't you go after a job in an industry that pays the maximum for the effort you have put? Plus back home there is a certain level of prestige that comes with bragging about working in certain companies.

depends on the company.

but be prepared to be used.