Because, even though it’s dark and cold, the Winter Solstice marks a turning point. Starting tomorrow, as the Sun climbs higher each day, the days lengthen while the nights shorten.
It is a point of reflection both literally and figuratively, and a time for optimism as we realize we have lived though the worst and have better times ahead.
Perhaps that’s one reason we celebrate this darkest time of year, lighting lights and "singing and dancing to drive the dark away."
We do it because the Winter Solstice also brings hope.