I have yet to see one major contract for an American company.
I know you're not looking at DoD contracting there.

As far as mineral and oil exploitation think that is because both Iraq and Afghanistan represent risk profiles far outside that for most Western corporations. The Chinese, OTOH, are known for their willingness to go to marginal places on marginal contracts, often with thin to nonexistent profit margins in the Western sense.

Iraq, for all the progress, remains far more violent and politically unstable than Nigeria, for instance.