They don't. They want it to come up in the morning. In many places there isn't enough sunlight in the middle of winter to have it up both in the morning and the afternoon, so they need to pick one.
From a safety point of view, probably sunlight in the morning in more useful because sunlight drives temperature. That means mornings tend to be colder than afternoons, and so are more likely to have hazards such as ice on the roads.
When you go with dark mornings, you are combining the worst road conditions with the worst visibility. When you choose light mornings over light afternoons, then morning is combining the best visibility with the worst road conditions and afternoon is combining the best road conditions with the worst visibility.
Another factor is that commutes tend to fall into a narrower time range in the mornings. The commutes back home after work tend to be more spread out. This tends to make the morning commute more dangerous, which further argues against placing the morning commute in darkness.