Something being true for forty years means it had been true for forty years, not that it was only true forty years ago. As you have seen from the graph I posted, car ownership has gone up significantly over that time, but there is still a very substantial minority - of mostly poorer, labour leaning, voters without one.
So Shami wasn't being patronising she was pointing to a widely accepted truth. And even is she was being patronising, the weather absolutely undoubtedly played a bigger role as her comments were made after all the votes had been counted.