Having grown up in the mid-west and then moved to the east coast after undergrad for my first job, I was shocked at how different the cultures were in regards to parental financial support. A few people have hit on cost of education and cost of living etc but I think one of the biggest factors is just the cultural expectation of self-sufficiency and working at a young age.
If you are talking about farming areas of the mid-west, those kids are helping with chores and working at a very young age. By the time they are in middle school, they are driving tractors and working. Every kid I grew up with either worked on the farm or held a job in high school and through college. Even though not all areas of the mid-west are still rural, many of these families still have ties to these roots and the expectations remain.
To say that it is for a lack of money, is ridiculous. According to Kiplinger's, Omaha has the most millionaires per capita of any metro area in the US and is home to 5 Fortune 500 companies. And although cost of living may be low and people live fairly frugally, a typical machine shed probably houses a $500k combine and has three $100k - $200k tractors, with a family farm of about 1000 acres. People from the mid-west have money.