In addition to the obvious negative effect on learning curves, I'd argue this dearth of "long-form documentation" has a negative impact on programming language and app development, as well as software usability in general (isn't CONTROL+COMMAND+SHIFT+3 for a MAC screen capture intuitive?)..
AI has become the new "teacher of record" to fill this documentation void, but it's very individualized and narrowly focused. There's no longer a shared mental model, where everyone has read the same books and are working somewhat off the same page. Ironically, it's probably never been easier to write a good tech book, but there's likely zero money in it and the search and AI giants are likely to hover it up and start serving snippets of it up for free before you see a dime, making people very unlikely to buy your book, even if you've written a technical masterpiece!