One aspect of it is that the lower density of the water, compared to salt water, makes the waves steeper and shorter in period (closer together). Also, there's more contact with land. I remember reading an interview with a world cruiser. She was asked if it weren't frightening to be out in the middle of the ocean. Oh no, she said, that's easy to deal with. The frightening part is the hard stuff around the edges. I know that on my own boats, the scary part is getting back near land or a narrow channel, places where there's a lot less room for maneuver or for mistakes.
As to the Fitzgerald, on theory is that she bottomed out on a reef in heavy seas. The reef was charted inaccurately, and in a huge storm navigation is much harder. And the Fitz had lost her radar by that time anyway. Wind or waves took it.
Chris Campbell