And I fully note that the book I linked to is exceptional. It won a oscar.[1] And was basically required reading at pixar, if I recall.
Papers are very condensed and probably scrutinized more than textbooks are, via the peer review process. Papers have to have proofs for any theorems, whereas textbooks might omit them (especially the less important ones).
Also, to be fair, a textbook might rely on a dozen different papers in the span of a single page (just taking key insights or arguments for the papers).
I would be interested in seeing the publication times for many text books. Empirically, we should see something in the difficulty in relation to the time it took to create. Right?
Edit, since I saw your point of referencing many papers in a single page. Don't papers do the same?
I mean, a textbook might take years to write/edit (on and off) But it takes at least a month (on and off) to write/edit a paper.
As it is, the code is often neglected. And rarely shared. Both bad facets.
And making a full text book that is executable is what I was comparing. That entire book is a program. I'd imagine that was much harder than the typical paper. Many of which are surveys and gloss over deficiency of the supporting code. (Again, I still concede the black swan nature of that book.)
Also, there is no incentive because of the reasons I stated (pedagogy to someone new vs. succinct explanation to expert)