You don't understand it because the mental model as presented by the statement is too simple.

Money can make LOTS of people VERY happy, up to a certain point. Supposedly after 80k$, after you've been relieved of basic stresses like rent and finding food, more money will make you less happy per increment.

If you are an unhappy person with a minimum of 80k$, then the bottleneck to your happiness is not money.

Merely more money doesn't make ALL people happy ALL the time.