GA works best for any given insurance company in the long run. No one insurance company wants to cover an enormous loss. But there are hundreds of shippers on that voyage, and so each shipper’s insurance company now has to cover only a small amount of the loss.
It’s the reason starlings flock together. A starling alone is subject to high chance of enormous loss (death) from a hawk. But swarming in a flock of thousands, each starling only has a small chance of enormous loss.