Why was much of Beringia not covered by glaciers during the last glacial period?

Although much of the Northern Hemisphere experienced extensive glaciation during the late Wisconsin Glacial Stage, much of Beringia remained unglaciated because it possessed a dry climate. This arid environment prevented the accumulation of the massive ice sheets that covered other regions, instead supporting cold-hardy tundra vegetation. This unique landscape allowed land mammals and, according to various theories, early humans to traverse the region between northeastern Asia and northwestern North America.1