Guides, manuals, documentation ... They all really need a practical application (of purpose) to give them real context.
I believe poor assembly instructions are a very different issue ! (the IKEA reference).
A good tool should explain itself ... A shovel, a hammer - they don't come with operating manuals - but technique, skill, etc they're another dimension.
In this day and age - rich media offers so much more than still diagrams and the written word. People have become more receptive to this form of learning. The trusty manual has become a necessary compliance delivery with the goods - but the usefulness of the manuals ??? Well, why put the effort in if you really don't believe is gets read, or if it makes a significant difference to customer satisfaction.
Who has read the booklet that comes with their car? Who reads the product disclosure statements for finance and insurance products.
You'll probably find the real use of the manuals delivered with tools, etc these days are more about legal covering of butt than training to use - making sure that if someone cuts their nose off with a power saw, that there's something documented to say its not a good idea to stick a running saw in your own face!
Remember the instructions for VHS recorders fro the 70's and 80's ... Those were the days.