So often in these tragedies one can see some reason - some possible logic in the crew's thinking, but this one has me beat. If indeed they were flying south-ish in the valley, they would have been heading towards the highest point towering a thousand feet above the requested. That peak is just a 'stone's throw' from the crash site.
Is it conceivable that for a moment each pilot was comfortable with the rising ground on their side - thinking they were simply to the side of a solid mass?
Having done the Innsbruck run for some years, I know only too well how a wide open space suddenly becomes a claustrophobic gully when one pilot turns the wrong way.