Why materialists are predominantly materialists

[Angrboda]

Chomsky once said something like, 'Before you start asking questions about 'physical' and 'non-physical', you have to define what physical even means.'

It's a good question.  Did he provide an answer?

My answer is that whatever is or isn't "out there," the human experience of it is purely experiential/idealistic.  In other words, the study of physics is a category of idea-- about the nature of and relationship among objects.  It doesn't really require a position on the underlying nature of reality.

Of course it does. Ideas as a something is opposed to ideas as nothing. That's taking a position. Only by contrasting the world of ideas with the world of things do you come up with the notion of "what ideas are." Relationships among objects is a category of idea but it doesn't explain what an idea is. Our experience is completely noninformative about the nature of ideas. The only non-position position about their reality is pure agnosticism. They could be material. They could be a substance in and of themselves. They could be illusions. By describing them as a substance in and of themselves, you're taking a metaphysical view about them as sure as materialism is. What's worse, you're defining them as the negation of the material. That's borrowing the concept of the material in defining the idea. It's an example of the use of the stolen concept.