In PST today, December 21, Sunrise was just before 8 am and sunset will be around 4:20 pm. Change that to PDT and we have sunrise just before 9 am and sunset around 5:20 pm.
The coldest time of the day tends to be in the morning before sunrise. On foggy days the fog is more likely in the morning than in the evening. When it freezes the roads are more likely to be icy in the morning. Even if the air temperature doesn't get above freezing all day there is a chance that sunlight during the day might heat the roads enough to melt the ice by evening.
Because of all this if you have to travel in the dark, whether as a driver or as a pedestrian or cyclist, you will generally prefer evening dark to morning dark.
In addition to the asymmetry between morning and evening weather there is also an asymmetry in traffic intensity. Pick any two random people and compare what times they travel to and from work or school.
Their morning travel times are more likely to be closer together than their evening travel times. Offices all start at about the same time, so you get office workers all coming at about the same time. Similar for elementary school start times, and middle schools start times, and high school start times.
At the other end of the day first you've got schools getting out which generally happens a couple hours before offices let out. Second, workers tend to leave work over a wider range of times than they arrive. You've got people who stay late to get something done (much more common than people who go in early). You've got people who do errands after work before heading home.
So at latitudes like that of Seattle permanent DST pushes the morning commute farther into worse weather and the morning commute is the one this is already the highest risk because it is the more concentrated commute and it is the one with the most overlap between adults driving for work and kids walking or biking for school.
Permanent standard time also is better for our circadian rhythms than permanent DST.
Most people here are too young to remember this, but the US tried year around DST in the '70s due to an oil supply disruption caused by war in the mideast. They thought permanent DST would lower energy consumption. It turns out it didn't have affect energy consumption much, but it was pretty much universally hated for the downsides I listed above and ditched after a year.