[FizzyWater]

My opinion only:

• Some people feel that reading across the entire width of a screen (e.g., a computer monitor, not necessarily a tablet screen) to be distracting.
• If I remember correctly, there have been studies done on the optimum width of a block of text for readability and comprehension - something to do with how much of a sentence your eyes can "grab" with a single glance, instead of having to move your eyes back and forth across the page. The same logic is/was used by newspapers - breaking up the page into columns to make the information easier to follow/digest.
• Some people think the 2-column layout is more like reading a physical book - and they prefer that resemblance (I assume these are the same people who like to see a page flip when they turn the page, too)