y no reverse lights?

how come our trailers dont have any reverse lights?, our tractor does, and even at that its usually just 1 light that most 4wheelers can not see.
im just wondering,
i no that when you are backing up to a doc in a loading area such as a warehouse we dont need them, and us truck drivers no that putting the 4-ways on usually means " look out, im backing up " but the regular motoring public see 4ways and think that truck is pulled over and is stopped. most dont no that we are going to back up.
i ask cause i dont deal with loading docks at all, and i have a sleeper and a 53, i usually back up to a dock off the street, or i most of the time i have to back in to our custumers drive way off of a street. and i think if i had reverse lights more people would be aware that the truck is backing up....