Maybe I'm hypersensitive to this because I work in building services but there's one thing confuses me about peoples desk setups in real life versus the internet. I've been in real offices. I've been in a couple of home offices. They don't have their desks facing into walls. For me it's the same principle as gym treadmill facing a wall you're meant to have a sense of going somewhere. It should be facing a door or a window. It's bad feng shui. You have no concept of your surroundings with your back to a door. Even in a small room you don't get to appreciate what little space you have looking into a wall.
Is this also an old idea that if you have your back to the door than you are unsettled as you are open to attack from behind, whereas if you are facing the door then you subconsciously feel secure as you are forewarned about any threat. Supposedly leading to better concentration.
I for one have an office, have had multiple offices and all except for two have faced a wall. I have also worked in many office blocks doing aircon balancing and yes desks generally don't face walls, but this is because of a lack of walls as they are open floor plans. Depending on the climate it is also a general rule that you should not position people closer than a metre to the outside wall of a building as temperate fluctuation occurs (sun heating the windows, return air for the aircon etc), making it very uncomfortable to work in. Chances are, if you have an office of your own in an office block (like separated by walls) you are most likely higher up the chain and therefore don't want your workers coming in unannounced and observe you watching cat videos on youtube during work hours. I guess this goes back to the forewarned concept.
It is also a space thing. if your desk is against a wall, than it appears to take up less room. If you have your desk off the wall than your floor space is reduced. So it is not always best use of space to have it facing a door.