Mostly because of hailstone damage, but also might be because it's simply too dangerous to keep driving.
There were a couple of occasions back in the UK where I stopped on the hard shoulder or sheltered under a bridge because the rain was coming down so hard you just couldn't see well enough to drive.
If it's a hard shoulder choice it's a difficult one because if others are doing the same you need to find a gap to pull into without running into someone else. Then when it eases off you have the problem of trying to get up to speed on the hard shoulder before joining the traffic flow without hitting anyone who's still stationary on the shoulder. Still, I felt it was safer to pull over than to try and drive at even 30mph because there were a lot of drivers still trying to go at 70mph or more!
Under a bridge is easer because at least you're more visible to cars passing you, but I did feel sorry for the woman who'd pulled in opposite me. She had some tall potted plants on the front seat of her car and so had her sunroof open. So much water was collecting under the bridge that when traffic went by too fast water sprayed into the car via the sunroof. The poor woman must have been soaked by the time she moved off.