Except that is exactly what the law says they must do in some cases. In some cases it is left up to discretion, or we are allowed to choose a U.S. company bid o

Except that is exactly what the law says they must do in some cases. In some cases it is left up to discretion, or we are allowed to choose a U.S. company bid over a foreign company, but government procurement does not work the same as private enterprise. OTOH, the scale we're talking about is also vastly different, and the companies involved are ultimately responsible to the taxpayers rather than just being responsible to their shareholders so there is more overhead and paperwork as well.