So why a total ground stop at Pearson today?

Many sources including the Toronto Star have raised the question of why a paralyzing ground stop was necessary at Pearson Airport this morning.  It has been a frightful frigid day and anyone can understand how the cold will slow down human activity. After all, humans have to ensure their survival before they can work. So there was a real issue. But other airports continued to function. Why a shutdown? Here is a medley of photos showing the jammed luggage carousel, crowded  halls and sleepy passengers.  Robert Palmer, a West Jet spokesperson, said the ramp was dangerous and it was not safe to put ground crew on it.  He called the cold weather extraordinary and unpredictable.