Wow. I am mightily impressed that the engines survived that.

Isn't the on-board radar supposed to pick up hail so that they can fly around/over it?

I suppose that is COULD have just started up when and where they happened to be flying, but would huge hail start out as little hail and get worse over time so that you have enough time to react? I lived most of my life in Florida, so I do not know much about hail.