‏There are many reasons why a person may avoid people around him and prefer to be alone but the most Famous reason which are Childhood trauma and Covid 19 and bullying resulting from 

1)Childhood trauma, such as abuse or neglect, can cause kids to feel scared and upset. This can make them have a hard time trusting others. They might want to be alone because they're afraid of getting hurt again. This can lead to social isolation and make it tough for them to connect with people

2)Covid 19: People became more alone after COVID-19 because of quarantine. And That mean staying home more and keeping away from others. Also, many started working or studying from home, so they didn't meet people as much. All of this made them feel more isolated until now.

3) bullying: When someone keeps bullying another person, that person will feel unloved and unwanted. This can make them want to stay away from others.