There is tight correlation between family income and the number of family members working.
The primary reason some people are making less than $50k and others are making $50 to $100k is work! People in the higher income brackets are working more than those in the lower brackets.
Families making $50k to $52.5K average 1.46 workers while those making $75 to $77.5 average 1.82 workers. This relationship is consistent from the bottom to the top.
Bottom line: People at the bottom are not working as much as people at the top.
Household income in the United States - Wikipedia, the free encyclopedia