Calculus (and the rest of math) is taught because development of human civilization depends on some people knowing it and developing it further. And if you don't start early it's hard to catch up not to mention developing it further.
And it's also training your brain (but that can be done by other things like puzzles or games).
I'd say this used to be true, but calculus has become a historical artifact even at some engineering fields. We have become very good at building abstractions. Matrix / linear algebra on the other hand is something we unconsciously do all the time for high level tasks such as rearranging UIs.
And it's also training your brain (but that can be done by other things like puzzles or games).