Breakage of violins in transit has been researched thoroughly, and as a result high-end violin cases are usually made to grip the violin high up on the neck, at the centre of gravity. It's free to move a bit around that point. This avoids the sort of flexing that snaps the neck or detaches it from the body.

Looks like the guitar cases causing this sort of breakage haven't taken account of the actual stresses caused by throwing them around. Simply making the case as solid and heavy as possible doesn't cut it - what happens inside the case is what matters.