Gov.uk has a max sentence length of 25 words
insidegovuk.blog.gov.uk
insidegovuk.blog.gov.uk
I spot-checked some stuff I've written, and sentences regularly exceed 29 words. Some of this would certainly be improved if it was shortened a bit, but I don't think most of it is "very difficult" to read. The study is a 404, but I'd expect there are other factors beyond sentence length – in particular, I wonder how much other punctuation marks such as commas, semi-colons, and dashes affect things, as well as general writing style(?)
As a reader, I'm not a huge fan of the "short sentence, short paragraph" style. BBC does this, and it's one reason I don't really like the BBC. There just isn't any good "rhythm" or "flow" to it – it's kind of hard to explain. I dislike the bullet-point style that some publications have been using even more (actually, I dislike bullet points in general, outside of some specific use cases).
If you read some older 16th-18th century works then they often have ridiculously long sentences that never seem to end. I have difficulty reading those. Old-fashioned spelling also doesn't help here.
There's certain contexts in which only long sentences really do the job though... I see some eye watering sentences in scientific papers all the time. Sometimes you can hardly comprehend a long sentence because the concept being described is simply difficult to comprehend.
This is partly because people tend to scan, not read. In fact, most people only read around 25% of what’s on a page.
I've got dyslexia and ADHD and several other attributes that make reading difficult.
Most people do not read well and many not at all.
$ echo "Google Analytics sets cookies that store anonymised information about how you got to the site, the blog pages you visit, how long you spend on each page and what you click on while you're visiting the site." | wc
1 37 207In the world of patents, multi-hundred word sentences are normal. There are regulatory reasons for that. Yes, patents are inaccessible, which suits the purposes of the people who write them.
This generalizes to the worlds of law and academic writing.
Besides all that, a sentence with many words in it may suit poets.
I have written very long sentences specifically to create a puzzle for my readers; I have done so specifically to convey a sense of complexity as a rhetorical technique; I do so in the service of my project, whatever that is.