I think the consuming device matters. A ipad or computer have much wider screen width. One column layout is too wide for them for average people to scan text lines quickly.
While it looks perfectly fine on a phone. Two columns layout looks terrible on a smartphone, the text is too tiny to read comfortably.
It would probably be even better if you can flip it left and right like a ebook instead of scrolling to allocate the content faster. But current design is good enough IMO. (Compare to reading a pdf on cellphone)
To display two column layout you need a tall screen, now wide. If you display two column layout on a short wide screen, you have to scroll it up and down in zigzag pattern to read one page.
It's about "One column layout is too wide" - if you zoom, it's not too wide anymore, also smartphones have narrow screen, not wide, and tablets can do that too afaik.
While it looks perfectly fine on a phone. Two columns layout looks terrible on a smartphone, the text is too tiny to read comfortably.
It would probably be even better if you can flip it left and right like a ebook instead of scrolling to allocate the content faster. But current design is good enough IMO. (Compare to reading a pdf on cellphone)