To use your example... Taxes are easy for the vast majority of people (claim the correct number of dependents, take the standard deduction, and you're done). For the rest of us, there are CPAs willing to do them for a few hundred to a few thousand dollars.

I say this as somebody who had to navigate the AMT rules for years in my 30s and hasn't used the standard deduction since college. In no way would I expect a high school to teach me personal tax law at the expense of a basic understanding of biology or literature.