Gotta be cheaper than buying new planes which would also have new engines. Generally there needs to be a pretty substantial increase in capability before it’s worth retiring an existing platform, especially in a logistics role where you don’t get as much benefit from the bleeding edge because nobody’s supposed to be shooting at you in the first place.
Not gonna lie, “enforcing the line between ketchup and tomato sauce” isn’t the sort of thing I’d expect the government to be into, but I guess I’m not mad about it?