I think it has to do more with forming a habit and finding comfort in that habit. A person, usually during winter, forms a habit of using blankets and finds it immensely comforting. This then continues even during summer when they need that blanket to feel just as comfortable. And once this habit kicks in, regardless how hot it is, people won’t find sleeping comfortable unless they have a blanket over.
Of course, this is a very broad and generic way of explaining this. But this is exactly the reason why I need blanket to sleep, regardless the temperature.
There is also a scientific explanation to this. It is believed, blankets help us regulate internal temperature during REM sleep. Then there’s also some theory that putting on blankets release happy hormones in our body – serotonin and dopamine. And since we like that happy feeling, we always sleep with blankets.Also depending on individuals and their age, the will, reasons and habit to use blankets can vary. For example, kids and teens and even the young people use put on blankets when sleeping out of fear of darkness. While as absurd as it may sound, psychologically it feels that if any danger comes, a thin fabric (hear sarcasm) between that danger and the body would provide a protective layer—one reason why we use blankets to hide our face and fear after watching a horror movie!