The answer to 'why is my soffit ice dams' is that ice dams form when snow on the roof melts, usually due to heat escaping from the home, and then refreezes at the roof's edge. This causes a buildup of ice that can prevent proper drainage and lead to water damage in the soffit and other areas.
Some common causes of soffit ice dams include inadequate insulation in the attic, air leaks that allow warm air to escape, and poor ventilation that doesn't allow the roof to stay cold enough to prevent melting. Symptoms may include icicles, water stains, or rotting wood in the soffit area.