Largely (and thanks to a great deal of disinformation emanating from the "big food" industry itself; supplemented by the generally shitty state of most public school eating programs) because people don't
understand "food": where it really comes from; how these ingredients come together; why we eat the things that you do; and most importantly, how we can take control of this whole process, at least on an individual level, and improve not just our healthy and well-being, but our general sanity (and over time, our bank balance) quite significantly.
It's one of most important life skills there is to learn... much more important than learning to code, or even to drive. Yet for various reasons, it's generally treated as an afterthought in our education system, and severely undertaught.