This is one of the most absurd tropes in capitalist societies where you literally need money just to exist. No only that, but money literally buys happiness because you can pay other people money to do things you don’t want to do, and that frees your time to spend on things you enjoy doing.
Money on its own doesn’t make you happy, but it certainly makes it easier to avoid many of the things that make people unhappy (hunger, lack of security, inability to care for your kids/loved ones, etc).
That’s a pretty good reason to seek it and hold on to it, even if the bare notion that “money doesn’t make you happy” is true.
Then there’s the fact that we’re innately and/or culturally programmed to get satisfaction from feeling richer than our peers. There are genuinely few people who don’t have this impulse in them somewhere. Good luck coming up with a functioning political system that doesn’t acknowledge this.