It looks like after suffering an engine failure it was difficult to judge the flare height on the snow and they hit before the pilot was expecting it.
Possibly one scenario when you would want to know your minimum sink speed rather than best glide and just fly it in glassy water style...not completely sure what would be best because that might provide quite a firm arrival versus flaring but one's visual perception could play all sorts of tricks on you and you might end up stalling and dropping if you tried to flare and did so too high.