Answer: There are different values of life. Not everyone has the same idea of life's purpose.
Explanation: As you know, people have different opinions. Some like peanut butter, some don't. Some love math, others don't. In a way, the same thing goes for the main purpose of life. People grow up in different kinds of households, and that can also mold what they think their purpose in life is.
Basically, everyone has a different idea and purpose living.
(but if you're really sad and don't see any purpose in life, you should talk to a loved one or hop on a sadness hotline)