I don’t think they are truly happy. They have moments of joy and things that feel good, but they live in a mileu of misery that they’ve just grown to normalize and doesn’t affect them much.
Happiness isn’t just being able to avoid sadness, that’s just contentment. It is difficult to explain happiness to someone that hasn’t been truly happy. When I used to do cocaine, those feelings were pure happiness, and I’ve never really felt something to that degree again. I think happiness as we know it is really just a modern concept, one that is enabled by our increasingly leisurely and stimulating life, that has vastly expanded the length and enjoyment of our childhoods. Maybe being happy is a lot like being a child, forever.
I think you might not have the best definition of what's happiness. If you go to some Amazon/brazilian indigenous tribe today, you will see happier people than the modern human. That is how many people lived in 1025. Even the people living from the land, they could not work the whole day all day, there was not enough things to do.
Nothing knowing that they could have an easier life also probably played a big role on their happiness. Unhappiness (and depression), I would argue, is probably a modern disease.
People are happy in Africa, Latin America and the poor parts of Asia now, many places people are happier than in the US actually.