Maybe just maybe the employer finds productive value in the employees they find with a degree (the whole well rounded part that makes up half the degree) regardless of major.
Again, with your thinking we shouldnt fund high school.
Most people don't need calculus or even much math beyond basic algebra either to live their daily lives\do their jobs. Or half the stuff we did in HS english classes when we spent a large portion of time analyzing literature. Or most of the history we learned, that clearly has no effects on most of our productivity as workers (as if adding cogs in the machine is the only benefit society could ever achieve). But we do all these things, and almost universally agree that it is a good thing we provide kids with this kind of rounded education.
Given your general tilt regarding such things, I am surprised you are into defending education as much as you are. Our current system mostly benefits employers because they either (1.) get trained workers or (2.) have a convenient way to sort "good" and "bad" workers from each other using education as a signal at virtually no cost to them. The costs, however, are born by individuals, families, and the public purse, like state governments.
All the risk and costs are on "the little guy" or public accounts and all the benefits are on what you normally consider those who need the help the least with businesses.
Frankly, I think we should stop subsidizing either the training of workers or the search for good workers that corporate America should be paying for on its own.
I would not "cancel" high school. I would just be more flexible if teenagers wanted to work instead, especially with the consent of their families, and/or replace most of the college preparatory coursework with vocational training. Why make a student who is either already leaning towards learning a trade spend 3-4 years on college prep classes, such as the history, literature, geometry, physical science, and calculus that you acknowledged is useless for all but a very small quantity of workers, wait until they are 18 or 19 to start that training when they could just go ahead and do it when they were 14-17 and start working sooner?
There are a small number of nerds who do benefit in the long-term from learning such science, advanced mathematics, or delving into the humanities. But that is a punishingly small cohort of students, and most people will barely remember any of it a decade later.
It used to be "universally agreed" that the Sun revolved around the Earth, too. Conventional wisdom is exactly what you want to buck in looking for market inefficiencies.
We are over-leveraged in education as a society right now.