I agree with your last sentence, but on the subject of positive portrayals of US armed forces, the studios actually have an incentive to play nice. The DoD will let film productions use real equipment and personal, but only after vetting the script and making changes as they see fit.

For example, the Transformers movies: https://www.wired.com/2008/12/pentagon-holl-1/

The general concept: https://en.m.wikipedia.org/wiki/Military-entertainment_compl...