Military planes cost more to operate. They’re not built for efficiency but for war. Airlines do everything to cut costs. Military planes are older, have specialized mx and crews have to be trained in war fighting. The military often leases out civilian flights to move troops because it’s cheaper.
That was my instinct. All my friends are obsessed with military aviation and their crews and super specialty.
You have good instinct and basic common sense. Sure you can use them as training flights, but are they “training” for the combat missions they’re supposed to be ready for? Flying into civilian airports and following federal passenger dictates for detainees isn’t necessarily the training they need.