Perhaps one reason is that outside of school math, computation is actually how most people do math, and to a considerable extent, science.

Don't get me wrong, I was a math & physics major in college, and love doing derivations and proofs by hand. But in my present job, if I have to solve a math problem, or perform an experiment, I reach for my computer.

As it stands, school math is limited to problems that can be solved by hand in "closed form," creating a stilted view of what can be done with math.

I realize that programming is not CS, but an introduction to computation, within the math and science curriculum, might be a way to make those subjects more interesting and relevant, while also providing some preparation for kids who might develop an interest in CS later on.