This may be obvious but, some things other than drive:

-Intelligence
-Income level you're born into
-Skin color
-Physical and mental handicaps
-Location- Job and education opportunities (have to afford moving -expenses)
-Drug and Alcohol Abuse (if you believe they're a disease)
-Succumbing to the poverty culture.

Not to say that there aren't alot of people solely responsible for their poverty because they lack drive. But like the excerpt says- we are not equal. There are the people that rose above poverty and when you think about it, required more drive than the average American.

To you it may seem like I'm apologizing for the poor, but you are probably viewing them, in comfort, through the glass of the white male system which doesn't allow for shortcomings. With the exceptions of racism and sexism, it's not necessarily wrong but rather a harsh reality that bears consideration.