Because most high schools do not offer business math, economics, microeconomics and macroeconomics. Most math teachers don't teach about check writing, loans, stocks and bonds, OR in my case, the parents insisted I was wasting their children’s time teaching those things.
(The rich parents said that they would teach their children. The poor parents will likely not know about such things. Thus, the rich get richer and the poor get poorer!)
The Native American parents were thrilled that I had their children ‘buy’ houses with ‘down payments’, buy cars, write paychecks by removing Federal Income tax, State Income tax, Social security and Medicare expenses. The kids were stunned at how much of their income disappeared in their paychecks! Then they made monthly budgets and wrote ‘actual’ checks for their bills. They learned how to write the check so they couldn't be manipulated for more money. They learned about interest rates, even though Native American people try hard not to use loans. They believe if the improvement is quicker than the interest, then a loan is justified.
These mathematical items could easily be included in 6th grade when they are required to learn about interest, discounts, and overhead (profit).
It would also help the United States to develop more entrepreneurs that build our economy and help it grow. Otherwise, entrepreneurs are most often only those children of parental entrepreneurs, which is declining!