The amount of resetting the postion of the eyes back to the start of the next line is much greater on a smartphone. I wonder if the greater effort of scanning affects your brain's ability to sigh and comprehend.
Newspapers and magazines have always formatted long text in narrow columns of 5-7 words. Admittedly I find it very irritating to read every now and then.
Most paperbacks have paragraphs that are about twice as wide (10 to 12 words) and it definitely feels more natural.
