new Land Rover Defender roof load 0 kg???

Hello Can someone please explain to me why the Land Rover Defender V8 has a roof load 0 (zero!) kg? I have been trying to get an answer from my dealer and also from the Genarla importer for weeks. Unfortunately unsuccessful. Can any of you help me there? This means in the figurative sense that if it has snow on the roof, I have to leave the Defender standing .-) Unusable and absolutely incomprehensible for me. Thank you and Gruss TR4A