There are a couple of reasons why someone might leave the bones in before packing out the meat. This doesn't mean these reasons trump other reasons -- lower weight, quicker cooling -- but they are reasons.
One reason is that it is quicker. What if you just don't want to take the time to debone the meat right at that moment. What if it is raining or a heavy snow storm is going on? Maybe your plan is to delegate that task to the meat processor?
Another reason is that theoretically the meat is less exposed to dirt and germs with the bone left in: all that surface area of the meat from the surface inwards is NOT exposed to drying, to buts, to bacteria, to dirt which is potentially exposed when you cut it open.
You might want to have the bones to make meat stock. I make about 18 cups of good elk broth out of each of my elk that I butcher myself. Part of that can come from just the meat trimmings, but it helps to have some bones in that pot, too.
None of this disputes that it is lighter to pack them with the bones out.