If I had to hazard a guess… those kids who get straight A’s in high school are the ones who are more likely to go off to study science, engineering, medicine, law, accounting - all these fields that require high brain power, and that parents push their high-achieving kids into. Once you have your degree in these fields, you can go off and make big money as someone else’s employee, be it as a university professor, or a lawyer in a big law firm, a doctor in a big hospital, or in R&D at some giant corporation. You can get one of these jobs and live quite comfortably. Now sure some of the folks in these fields can go into private practice, or start their own law firm, or invent a gee-whiz gizmo and start a company. But you can still do quite well without “fully participating in the American dream” like that.
Less so for somone who had poor grades - the university system definitely selects against them, and it’s hard to slide by in, e.g. engineering with poor grades. So if you end up defaulting to “business” or “communications” you’re less likely to find the same kind of lucrative career working for a big company that pays you very nicely to work 9-to-5. So maybe for the people who had less impressive grades and are now stuck in low paying, boring jobs, there’s maybe a bigger incentive to seek the independence and perhaps bigger rewards of starting their own business.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.