People are always complaining that schools don't teach them how to do their taxes, but for most people doing taxes is a combination of addition, subtraction, and following a page of instructions about which numbers to copy from one piece of paper to another.
Imagine trying to teach 16 and 17 year olds that are going to grow into adults that struggle to copy numbers from Box A to Line 3 and then add them correctly the difference between t-value and a t-value.
(I also believe the average person should have a better understanding of probability and statistics ... but we're still working on getting the average high schooler an understanding of why 1/2 + 1/3 is not 1/6 and why you don't need a calculator to calculate 7 * 0)