There's some influence from graphic design, responsive design trends, and some line length studies (not all conclusive).
If you're specifically referencing articles (where reading is the primary focus), there's some studies (a bit dated, and some secondary reference links are decayed) that look at optimal line length. Here's one from usability.gov:
Reading Onscreen: The Effects of Line Length on Performance
They measured readability by character count by line:
Dawn Shaikh (2005) reported a study that examined the effects of line length on reading speed, comprehension, and user satisfaction when reading online news articles. She had 20 college-aged students read news articles displayed in 35, 55, 75, or 95 characters per line on a computer monitor This is equivalent to line lengths of four, six, eight and 10 inches on a 1024x768 pixel resolution monitor using the Arial font. Her results showed that passages formatted in the longest line length (95 characters per line or 10 inches) resulted in the fastest reading speed.
If you notice, it doesn't say comprehension, but speed.
And an paper (abstract) from International Journal of Human-Computer Studies
A medium line length (55 characters per line) appears to support effective reading at normal and fast speeds. This produced the highest level of comprehension and was also read faster than short lines
If anyone can find some more recent studies, please post an answer.
Influences from graphic design (yes, it's not ux)
There's also a background influence from graphic design here. As web typography started to get more direct input by graphic designers bringing their print background to the web, you have references to influential type teachers such as Robert Bringhurst: The elements of typographic style
“Anything from 45 to 75 characters is widely regarded as a satisfactory length of line for a single-column page set in a serifed text face in a text size. The 66-character line (counting both letters and spaces) is widely regarded as ideal. For multiple column work, a better average is 40 to 50 characters.”
(my personal observation, not a study): I notice a trend towards bigger type and consistent characters per line with increased line height as the columns can start to get wider in relation to viewport changes, like tablet modes. It seems to scale.