Apparently the highest death toll on Snowdon is up the Llanberis path in winter. Looks innocuous enough and is probably the easiest route up, but if you slip there's areas where you won't stop.
Helvellyn is the same in Winter too.
People ignore the conditions and equipment requirements notices in all the car parks and still go up. Even with the right gear, it can get hairy very quickly and even worse if you`re up there with the wrong gear and aren`t used to the extremes.