Because people consider lighting when they live in a house, and they all want their houses to be bright.
Based on geographical knowledge. We know that China is located in the northern hemisphere of the earth, and most of its areas are in the northern temperate zone.
That is to say, the sun is in the south all year round, so the south-facing side is called the sunny side. It has good lighting and long lighting time, and is suitable for human habitation.
The north-facing side is called the shady side. There is no sunlight coming in. It is cool and suitable for food storage.
If the house is transparent from east to west, according to geographical knowledge, the earth rotates from west to east. The sun rises in the east and sets in the west. This will cause the house on the east side to have sunlight in the morning and the house on the west side to get sunlight in the afternoon. Neither of them gets as much sunshine a day as the south-facing sunny side.
Therefore, houses generally have windows facing north and south, so most of them are transparent from the north to the south.