Create a demand, yup, they steal them, they sell them on Kijiji or to scrap yards, Body shops will buy them off the scrap yards and even insurance companies will tell you "used one at this scrap yard, same color as your truck" instead of buying one new. etc. I guess rear ending is one reason, but if you get yours stolen, you still need to get one and have it painted to match your truck, so, body shop gets the business, here the insurance sends you to one of there body shops to get the evaluation, the body shop will call the scrap, find a replacement door, figure in painting it, etc and tell the insurance the cost to get the truck back up with a door. If they can't locate one, they buy one new off the dealer or replacement parts distributor, still need to paint it color match to the truck, end of the day, the stolen door gets used in the system. Most don't etch there parts on there trucks, mine are, but its not hard to grind that off. My truck has 20 micro transmitters in all the most stolen parts, there about 1/2" in length and 1/8th in size and are dissimulated in those parts, if my tailgate gets stolen it can be traced back to my truck, my tailgate I think has 2 hidden inside, Also, my insurance has me install 6 transmitters inside my truck, again dissimulated all over the truck. If it gets stolen I call the tracking company and they go get the truck. Sounds crazy, but its what needs to be done in my area.