Why is it that night falls, but day breaks?

Because as the sun sets, darkness follows it - falling from zenith to horizon. In the opposite sense, rays of sunlight radiate upward, breaking or cracking the enveloping darkness.

Because night falls down into the sky over time, slowly and peacefully, which capture everything night symbolizes and means. Night symbolizes peace and rest. The night symbolizes calmness.

The day, however, symbolizes a rush of energy. It symbolizes a fresh start, you can go out and run around the entire planet! The day symbolizes energy. So the day crashes into the sky; it breaks into the sky.