I think that's because you have multiple factors with thin smartphone glass. The harder it gets, the more brittle it becomes. You probably won't be able to cut into it even with a pretty sharp knife, but if you were to drop it at the right angle it'd shard into a billion tiny pieces.

I have no idea how automotive glass differs, but I imagine the difference in weight and thickness requirements does impact things a lot.

This reminds me of the unfolding problem of sun roof explosions.