Looking from the religious point of view, People complain because basically man has the in built genes to be unsatisfied.Man was said to be created a perfect being. But when he chose the sins of wanting to be as God then he chose to pass this craving of not being satisfied to generations past , present and future Man is always seeking for more. and this is why we keep on complaining.
Satan was created a beautifully being., but he too complained that he wanted to be like the Most high to set his throne in the North. You can find this somewhere in the Book of Issiah, and man is said to be like his father the devil. And only the saving power of Jesus can change that
People who do complaining do not want to spend time to change things, they would like to be a God to speak the word and get things change without expending any energy. However they should learn from the creator.
He did speak the word and make things happen, but in creating his great master pieces man and woman he did expend some energy and used his hands to create them. Like him we should expend some energy and time to use the resources we have around and change some of the things we murmur about.
Then we must also trying to acceptance some of the things we cannot change or get other people to change. These differences and circumstances are what goes to make the world such a diverse interesting places.
If every thing in the world was perfect man inherent genes of not being able to be satisfied would still find something to complain about.