Why do the mountain goats prefer the sparse alpine conditions created by the eruption, over the more forested areas?

From the text:

Mountain goats prefer sparse high alpine conditions, and the volcanic blast zone of Mount St. Helens created what Nathan Reynolds, an ecologist with the Cowlitz Indian Tribe, dubbed a “pseudo Alpine” area at about 2,000 feet. That elevation is much lower than typical alpine habitats but it is nonetheless devoid of forest canopy and the thick underbrush that can hide mountain goat predators like wolves, coyotes, cougars and bobcats.