If you think the DIY books are bad, try taking trade courses at your local community college!
The text and the art are often done by different people. Neither the artist, nor the editor know anything about the topic.
The sad fact is that the publisher relies upon complaints from the customers to do the editing for them. Then, maybe, the errors are corrected in the next edition.
It's unfortunate that folks see something printed as if it were infallable and wise. The simple truth is that anyone can publish everything, and never be held to account for it.
My NEC handbook has artwork that directly contradicts the code text right next to it.
One major publisher (Time-Life) told me that Canada doesn't allow the use of wire nuts - which is news to the Canadians.
Let's not also remember that the internet, according to the media, is a frightfully unreliable source of information.
