I dont understand why people always complain that life sucks?

A lot of people complain their life sucks, they have nothing to live for, life sucks in general etc. There are so many things you can do, join sports-or social clubs, read and inform yourself, travel and meet new people, create art like music or drawings, work to gain more money, flirt with dozens of women , become competitive at something or partying. Why are there still so many cynical / pessimistic people out there, who call the world we live in a failure?