I imagine these people have degrees in engineering beforehand.
For the most part people dont just jump into a specific job in the military. They aim for that job and get trained how to do that job with college level education for said job. It looks very good on a resume as you might guess.
Another reason people join the military is the drastically reduced cost of schooling after 4 years and the schooling programs inside the military, plus the general job experience is great to have.
Im still thinking about the military myself, either Navy, Air force, or Coast Guard. I refuse to join the Army or Marines.