Because computer science isn't about programming? That's exactly why a simple and elegant language should be chosen, one that allows to express the concepts that are taught. Java is such a horrible choice that it's laughable that it enjoyed this success at universities.

Yes, a simple language is better to teach CS. CS is not just about programming, but I think CS is about programming too and having a reasonable level of programming is useful.

If I was a teacher and I'm going to teach someone what a linked list is, or what a binary tree is, I can of course use natural language and drawing, I can use abstract algebraic concepts.

But the student should be also able to construct said structures and observe how they work. The same for any other concept.

Yes, and that's why a simple language is always preferrable to Java. It doesn't matter if a student has previous exposure to programming languages if this language can be taught in about two or three weeks worth of class.