This is probably related to the “get more parts from disassembling car” issue. Car components are simplified, and this includes the car body. Obviously there’s more to a “square” of a car than the usual frame and quarterpanel. There would also be glass, wiring, plastic trim, circuit board (for window and door controls), 12V window motor, rubber conduit (for where the wires leave the door and enter the rest of the car body), etc…
This is far into the future and I prefer they fix the bugs first before making the game more complex.