For many subjects, most kids will end up never using them. But, we have no way to predict which subjects will be useful for which kids. Without the ability to do that, our priority is maximize each child's opportunity. We never want a kid to be in the situation where they would have been interested in a subject and a career path but never ended up discovering that and using it because we didn't expose it to them.
So we teach some of every subject to every kid. That way no matter which path they end up following, they are as prepared for it as we can make them.
(Also, yes, I agree that math is good general training for cognitive rigor. Also, numeric literacy is vital for all adults since we live in an ecomonic world and participate in a democracy where statistics are necessary to understand policies.)