1 It feels cozy
Humans love to feel safe and secure. During winter people lock themselves up and watch the world through windows. This gives some people the unconscious feeling of safety and security.
2 Bonding with nature
Walking in a park or beside the sea can improve the mood. Humans love to bond with nature and walking in the rain is one of the activities that allows them to do so. Some people love rain but not winter.
3 Body image problems
Many people with body image problems hate summer because they have to wear clothes that show their flaws. A very skinny person, for example, might hate wearing a T-shirt that shows how thin he is compared to his friends, but in winter he can easily hide behind baggy clothes.
4 Humans love change
Right before the end of the summer many people start to miss the winter. The same happens during winter where people start missing the summer. People love to change, and as they get enough of something they start feeling like they want its opposite. See also why some people love routine.
5 More relaxing
In winter there is less noise, streets are emptier, and they look cleaner and calmer. Walking in the street during winter can relax the mind and help people get rid of stress and anxiety.
6 Lazy ones feel good
Lazy people who hate to get out of bed usually find a great excuse during winter. They feel less guilty by claiming that they are just staying home because of the rain or the bad weather. The same goes for those who aren't that social.
7 Feeling that they are not missing out on anything
During summer a person can easily feel miserable because of believing that he is missing out on great outings that are being held somewhere he doesn't know about. During winter, however, it becomes obvious that most people are just staying home and that nothing is going on out there.