If you think rich people can't be happy, don't think poor people with low incomes can be happy.
We need to accept the fact that we live in a pragmatic world, where money and material things determine almost everything from happiness to satisfaction. So, rich people may not necessarily be completely happy, but they are certainly much happier than poor people.
Those who earn less money and say they are very happy and satisfied with what they have. It's not necessarily happiness, but simply because they know they have failed and resigned themselves to their fate. Trust me, with people like that, if you give them the opportunity to get rich, their greed and desire will definitely arise and they will want more and more.
Iranus is cooking right here.

I agree with you, they're failed and just accepting their fate instead of keep trying until their last breath. Their happiness are mostly illusion, most of those people are full of bullshit. Whenever you discuss about expensive stuff with them, they will said "Anything is the same, I don't need to have a Lambo to make me happy, I have
auto rickshaw, they both have the same function".
There's a difference between happy person and loser, the real happy person is a multi millionaire who can afford rich lifestyle but he choose to live frugal/minimalist. While loser can't afford rich lifestyle and claiming if he's happy with his life.
The biggest lie the rich ever told was "money doesn't bring happiness", that has to be the biggest lie ever told. Money DOES bring happiness, because all unhappiness that are unrealted to money, can be either be same or better with money. Love pain? Doesn't change if you are richer. Trauma from childhood? Worse if you are poor. Basically you need to realize, money doesn't change anything and we should be considering how things could change and not return from it for the situation to change.
So long story short, any bad feeling you have could become very troublesome when you are poor, and be better when you are better. So it should not be complicated and needs to get greater for the time being, always want more money.