The glass cracks from a corner drop because the aluminum flexes and/or deforms much more than the glass, effectively focusing the force onto a small part of the glass's edge, which is the weakest part due to the hardening. Increasing stiffness and decreasing deformation spreads the force out across the edge, multiplying the effective strength.

There's a reason why cracks almost always seem to start at the edges. In the most severe cases of direct impact of the face on a sharp/hard protrusion, you get a radial crack pattern, but by my estimation those are a tiny minority.