How many of todays lawyers and politicians would volunteer for the Army?
Depends on what it has to offer.
Admittedly, more of my experience and knowledge is on the medical side and less on the JAG side.
Every profession has its own professional progression. The medical profession has a long term of internship during which the new physicians just barely survive financially the first years of their profession. So why not parlay your medical degree into a military commission and turn your internship into a financial coup?
Do JAG types have a similar career path? I simply do not know.