The parts of life you enjoy are exceedingly fleeting compared to how much you either dislike or feel negative towards. Most human pleasure systems seem to follow similar patterns to the male orgasm with a disproportionate amount of effort and agony endured in both desiring and achieving this small amount of joy. The human mind is exceedingly specialized at focusing on the small amounts of joy and not the massive time spent into obtaining it, so on a moment-by-moment basis you are less happy than you remember.
Considering how positive most humans are, and how much science and studies constantly show cognitive biases, it would seem more likely that pessimists are the more objective-minded people. And not all pessimists are the stereotypical depression-monger shown in media. Anyone with a pronounced negativity bias would eventually shift to hard nihilism, if anything.
My #2 touched on this, but yes. Pessimism is more about the bad out-weighing the good in reality than there being no good.
Humans think they are happy because evolution would usually cull the unhappy, suicidal/disillusioned ones who refused to play the procreation game. Even on a less philosophical plane, the human brain and senses can be easily distorted by things like optical illusions. Not even ignorance equals bliss because at least part of the brain is aware it's unsatisfied; animals would be in constant bliss if this was the case. The sentiment is heavily stigmatized by society and often treated as either a sickness (depression, psychopathy, etc.) or a juvenile/pretentious act from misplaced feelings or desire for attention (the common ridicule of Metal music, goths, most negative TV shows or films with unhappy endings). This is all to enforce the strength of the herd.
I think it's more likely that a pessimist is more experienced in talking about that which they disdain rather than talking about sports or the weather or what they do on their weekends. People usually stick to their strengths. I'm nearing anhedonia with only brief spits of joy, so I don't need any conscious design to remain dissatisfied. I don't have any good responses to this one.
Psychological pessimism would be what most people assume is Pessimism, while philosophically it's more structured and based on all of life being negative rather than just their personal life and environment being bad.
If everyone had someone to which they could look down upon and feel their life is worthwhile because it is better than this other person's, then the entire planet, and maybe the universe, would only have 1 suffering entity. And that concept makes no sense to me since so many humans in what is considered better circumstances find life tormenting enough to warrant suicide. The rise of depression in these lofty life circumstances would seem to imply that the satisfying of the basic human condition isn't enough to be happy anyway. And these conditions aren't even standard across the planet, let alone for any long period considering the likelihood of human extinction and/or natural disaster.
Hopefully I was succinct enough because I'm not very articulate in these matters. I've yet to convince anyone to my views on these matters.