This is a regional thing, not a "US" thing. There are lots of Dug fir trees (60-120 ft tall, often with shallow root systems. Also many power lines are above ground elevated lines, but shorter then the trees. Most power generation comes from hydroelectric, so plenty of power generation, but in the US Pacific NW, it doesn't freeze too often. Most of the time it is just wet and rainy all winter long. So two things: 1. people are willing to attribute power loss to storms 2. Trees are not generally used to such cold weather, so they will break and snap in this weather.

I'm not excusing such power outages. But this does come from a specific material reality.