Why do many people here seem miserable?

Often once in a while, someone would post something here seeking some hope like, do "things get better." But the responses are often harsh. I feel they are coming from the people that have given up and are full of spite. The positive responses are also getting downvoted by such people. When someone simply said, "I am thankful and happy with my life.", they get downvoted?? I thought this sub was to motivate people and explore the complexities of Life.