Because human body want to live despite our idiocy. When I see people like this I think that they sometimes have really strong bodies and good genetics in order to walk weighting over 130kg.It's really a waste,they could be some kind of atheltes or just enjoy life walking and running and jumping with a smile on the face like simple human being.  Instead they chose to live like disabled. It's beyond the stupidity,I think it's something interesting to study for the survive of human beings.