It never occurs to them that they too can become wealthy.
If it does occur to them, they never decide to become wealthy.
If they do decide to do something to improve their financial lives, they procrastinate, sometimes all their lives.
They cannot discipline themselves to delay gratification, to resist spending everything they earn a bit more besides.
They operate with a short time perspective. They think and act day to day and month to month instead of planning ten and twenty years into the future.