Yep, I agree. And I agree that designers can't "code", but to be more specific, it's more that they shouldn't be implementing functionality. So if a designer is designing a calculator, and the calculator returns 1+1=3, then the designer is not liable for fixing it.
On the other hand, if by "writing code" we mean the literal act of writing something that both a human and a computer can understand, then that's a different question. Designers need to express nuance, and GUI tools are limited in their ability to handle complexity. There's a reason visual programming tools haven't overtaken code.
What I'm getting at is that there very well could be a "language" specifically tailored for UI/UX designers, that allows them to specify their design decisions for the presentational layer of the application. If you had such a language, you could create a toolchain on top of it, which produces real code for developers to consume however they wish.
I'm (slowly but steadily) working on this exact thing: https://matry.design