"Why does Tire Rack recommend narrower tires for winter use?"
It's all about physics. Wider tire sizes have to plow through the snow which causes more resistance and a tendency to float. A narrower option, with a smaller contact patch, has more weight per square inch that helps the tire cut through the ice and snow.
In addition to the increased winter capability, there are other advantages to a minus size winter / snow tire. In most cases, narrower tires have a lower price tag. The advantage will apply in cases where you're purchasing a Winter / Snow Tire & Wheel Package with smaller diameter wheels. By decreasing the wheel diameter there's an increase to the tire's sidewall that keeps the overall diameter very similar between the two size options. As an additional benefit, the extra sidewall provides more wheel protection from damages that can occur from a pothole.
How do you know what the correct tire size is if you're going smaller? Your vehicle manufacturer will typically have options listed in the owner's manual or on the placard found on the the inside of the driver side door. Also, when you shop by vehicle we provide an extensive list of minus size options for your vehicle's winter driving needs.