Things can always be improved. We're it not for the drive for improvement, we might be content with things we define as being far lesser now.
basically people who were too happy with the same thing all the time got killed en masse in the caveman days and now it means we have a hard time being happy with what we have cause that was the brain type that survived enough for evolution to take over.
something something itoko
wait I mean itoko*
Evolution slowly weeding out happiness...