You have message channels, for a while. Open channels and broadcasts. Proximity to civilian services.
And then, in a fingersnap, it's gone. Encryption is pricey, and even at its best the mere time and place of an intercepted transmission can tell you a lot about where someone is and what they're doing.
It's a cost too high for letters home. Reassurances or apologies or just-in-case last words become things you need to carry, claustrophobic feelings-companions of the worst kind.
Not being able to feel anything outside of the context of fighting - at least not anything you can do about - does horrible things to a person.
So as much as any given squad may take the piss out of "Mail Mercs," they're dead silent when the letters go out, when the care packages make it through.
But that's probably not enough to sell you on it alone, unless you're a saint.
Is the pay good? Sure. Is it good enough?
Well. Those letters and packages still have value to opposing intelligence, and they can intercept them from your hands just the same. Pirates, mercs, and other rogue elements want what you have, for blackmail or simple value alone. You're never going to be treated like a protected noncombatant in the same way a medic would, so any given destination could be filled with jumpy soldiers or overseen by a commander burned by a spy pretending to be something just like you mere days before.
Maybe it's a job for you if you can't make up your mind between infiltration, diplomacy, or the front line. Maybe it's one if you have a deathwish.
Certainly not a job for anyone who wants to go down as a hero. Even if you deliver a peace accord. Maybe the politicians and generals on either side will walk away with statues or notes in a historical textbook, but not you. You're a verb, an action, the means to the ends for others.
Near-certain death, a fat paycheck, and knowing you kept some other people just as forgettable as you just a bit more human.
Can't understand 'em at all, but hell I am glad they're out there.