I really don't know what the designers (using the term loosely) of these units are thinking of, when it comes to lighting. We have a porch light on our Denali fifth wheel, but it is on the hinge side of the door, so as soon as you open the door, it blocks the light on the stairs.
We have friends who have an Aerolite with one of those large circular exterior lights, but the switch is nowhere near the door. It is at floor level inside their trailer, below the fridge.
Only explanation that we can think of - it saves about 8 feet of wiring.
I might add a solar light like some showed on a previous posting.
2011 Denali 262RLX Fifth Wheel
GMC Sierra 3500HD Gas