This is a question of health and civilization.
Doors and windows are different. The opening time and frequency of windows depend on the seasons, so you can open them for a while when they have or will not have an impact on your health, and when you need to change the air.
And the door is * * * people in and out, and it has to be opened and closed several times a day. Kang is for people to rest. When they rest, when they are blown by the wind, they are prone to catch a cold or even more serious diseases.
When the door is facing the kang, the wind can blow directly on the kang when it is opened, which will have an impact on health.
Moreover, the bedroom (with kang or bed inside) is generally private and should not be seen by ordinary guests. It is not always a sign of civilization to let others see their privacy or see others' privacy at will.
Generally speaking, rural houses have a hall (equivalent to the living room of a city building, not a separate building), which faces the door (entrance door). Go through the main room to get into the bedroom.
Nowadays, urban architecture generally pays attention to several rooms and halls. "Hall" at least refers to the living room, but whether there is a restaurant is another matter. Similarly, entering the bedroom requires going through the living room.
There is an idiom called "entering the house", which literally means that you can enter the house only after entering the room, that is, you must enter the house first.
As for the meaning or explanation of this idiom and its part of speech, I won't go into details here.
For your reference, I also hope that when you encounter various problems, you should first pay attention to other disciplines and think with your brains.