Because at least one of every car made should survive somehow. I get really depressed by the throwaway nature of cars these days - my Mercedes was worth nothing here, but if I get really pissed off with it (see Spring hasn't Sprung in maintenance) then an exporter will pay £150 for it to send it to South Africa.
Even as an unexciting car, if it needs so little, why kill it off?
(My XM needs about 3-4x it's value in repairs, but I still hold on to it...)
Richard