Look closer at the ranking of states. This isn’t about weather or external causes. Wisconsin and Minnesota have much worse weather in the winter and are almost as dark in the winter as Washington with similar death rates, but their rates are much lower than Mississippi and Alabama who have no snow and more sunlight in winter. The three are lower even than Arizona, which is usually sunny and rarely has snow.

External things like how many miles are driven on average by the people in the state is huge. Also things like speeding culture, average car safety (poor states have shittier cars or old trucks), and road maintenance are all big impacts, too.