The BOB is usually limited to a limited armed response, and anyone that has to Get Out Of Dodge (G.O.O.D.) would be better served in getting loaded and moving, rather than finishing the preparations such as loading magazines, finding spare batteries for tactical lights, and so forth. Also if you are bailing out with only your BOB you are pretty limited in responding to a threat, and rather than try to fit everything in one big bag, it is easier to move with two smaller bags.
While avoiding any type of confrontation is the best bet that cannot be guaranteed if one is in a situation that means they have to bail now, they have no time to pack or load a vehicle, and that everything has gotten pretty far out of hand, pretty fast. It is no longer the brown stuff is about to hit the fan, but it is coming like a cyclone right at you. It is you ether were not paying attention, or something delayed your departure.
About a year ago, I realized that for me to field a loaded rifle against a threat would take 5-to-15 minutes. The rifles were in the safe downstairs, and all of the magazines and ammunition were upstairs, pretty much the same story for the shotguns. I would have to get the safe open grab a rifle, run upstairs find magazines and the ammo and load the magazines. Everything was organized and secure in case I needed it, or so I thought. It was in fact too secure.