I had an idea some time ago about why people don't feel satisfied (and why they default to not feeling it, as well).
From what I know of non-sapient animals, they don't strive for anything other than what their instincts tell me: to eat and to reproduce. It is what we, human beings, would call their life goals; they don't have any more than that.
Humans, on the other hand, possess several abilities that separate them firmly, mind-wise, from the rest of the animals: imagination, logic, major memory capacity, ability to exchange massive amounts of information in a relatively short timespan etc. Humans have a hold on the past as well as a grasp on what the future might hold along the perception of the present, which is a lot of information to have a grip on at any given time.
But we're still animals. At our core, we still follow the two basic instincts, dulled or inobvious as they may have become for many of us. Left outside the civilization, we still retain some of our learning abilities but mostly remain (or don't grow out of being) wild, closer in mind to the wolf than to the man.
Could it be, then, that the dissatisfaction with the world that we have comes from the pressure that we feel from the society's view of being human?
Think about an average office worker. Dull as it may appear to so many of us, it's a tenuous job that requests of the worker to follow a lot of codes along with the "human code" (the morals, the society's rules, the laws etc.). An office worker is required to dress properly (which means they have to use and obey the sense of style), speak in a non-offensive manner most of the time (which involves conversational rules as well as the knowledge of the social hierarchy), produce what is required of them (which uses skill, time, effort and mental energy) as well as many of the smaller things, like not being late (work ethics, subordination, public shame) after being stuck in traffic (driving skill, coordination, traffic law etc.) and the like.
That's a lot to take even for a seemingly meager office worker. Then there's interpersonal relationships (which may range the whole nine yards), hobbies (to relax and decompress), travel (one of the recent things for humanity), worldview being constantly challenged...
As we feel the pressure, our minds run astray with the fantasies of a better life.
When our self-esteem is substantially challenged, we turn to extensive fantasies of ourselves to have our ideas of our selves from shattering. The same, I believe, happens to the idea of life that we have. The less we believe we're capable of, the more we imagine ourselves doing, again to be challenged to keep up with what should be, this time by ourselves. Sometimes, from this self-race come great things: music that survives ages, names that everyone remembers, events caused by humans that remain in history books. Sometimes, failure comes first, one way or another. Sometimes, something gets done, but not to the extent of our pressured animal minds. Regardless, the race continues, as the pressure doesn't fall.
In other words, we carry on our shoulders than whan any animal's ready for, so we push ourselves to compete with our ideas of what should better be.
That, at least, is my theory. What do you think?
By your theory, for humans' dissatisfaction to cease, we must revert back to a time with little to no expectations. However, these expectations were wrought from the rules of society which were created to maintain the general welfare. Humans are relative to non-sapient animals, however we are not the same. We cannot live the wild life of a wolf, else we become discontent and our full brain capacity unused.
Take for example, Lord of the Flies. Now obviously, the point of the book was more align with the Robbers Cave Experiment, but my focus is how the boys established a government (as result from social priming) and the disastrous results of its failure. When laws could not be properly enforced, they fell back to savage behavior driven mostly by the instinct to survive. (If you reread the book's summary and imagine it's a documentary of wolf pack interaction, the instinct driven actions are apparent.) Now the word "savage" is relative to our definition of being human, but I use it mostly to describe the general unhappiness of the boys. They were dissatisfied with a simple life of hunting/gathering and without proper laws, quickly fell into chaos.
Humans are naturally incredibly more perceptive than any other animal, thus more laws are needed to govern the population. The more intelligent the animal, the more needed to maintain "peace" (see: a colony of bacteria vs a pack of wolves). People are discontent and pressured by society, but not because people weren't meant to live in a society of this kind. Humans are driven by their instinct of survival. Naturally, our minds link successful people as those with the highest fitness (the wealthy can buy good food and shelter, able to alter appearance to attract potential mates, the symbol of status able to attract potential mates, etc).
Thus, many people falling short of this image of success and survival, are left unsatisfied.