There is a limit in physics here as the harder the material it is the more likely it will shatter (Wood Vs Diamond).
So you end up with two needs a soft glass to be more flexible (but is easy to scratch) or a hard glass which is very difficult to scratch (but can shatter when hit on the corner or edge).
Gorilla Glass solves the direct hit and scratch on the surface by being very thin and flexible and having a very hard surface across the face. It gives up its' protection when hit on the corner or edge thats when the phones frame needs to be able to cushion it.
But even here, there is a limit of what the phone frame can protect or in its self can amplify the bang making things worse (poor design or just bad luck). Which it's wise to have a case or sleeve to deal with the simple bangs and mishaps.