The beds got tapered for lower drag = better fuel economy. That is, apparently, more important to the OE than end user utility.....
There's plenty of pop-top campers out there that will fit your truck. We bought one out of a 2nd Gen Tundra that fit our '96 CTD fine. Have a look at the Wander the West forum for pop-top camper intel. There's an on-going thread there where campers on CL get posted.