Why do all these tools pretend that knitr / R Markdown never existed, and that they have invented some novel concept? I looked through the docs of Quarto, Jupytext, and now Codebraid, and none of them mention prior art.

There's a long legacy here, it does nobody any good to disregard it. Maybe Knuth is well-acknowledged for his invention, but I think for instance Yihui Xie is a little under-recognized.