Sans-serif is typically not a very good fit for body texts. The line-height is also set too low, makes it harder to jump to the next line as you try to find which one it is.
The font of this article is bloody awful though, I'll agree with you on that.
Sans-serifs has been a popular choice for body text on posters, backcovers (of books, albums, board-games etc.), user interfaces, instruction pamphlets, social media, blog pages, etc. I honestly have no idea where a recommendation such as this could originate from.
Sans-serif type became the standard in on-screen computer contexts in no small part because at 75–100 PPI resolution, monitors just couldn't render delicate features particularly well; even good anti-aliasing is going to turn the serifs on 12-point text into gray smudges. Computers just did better when you went to sans-serif fonts, particularly ones designed with relatively high x-heights and big counters like Verdana.
For example. It is easy to imagine older print technology being prone to ink bleed (particularly on mass print media such as books and news papers) which becomes very visible on small the smaller font-sizes prominent in the same media. I can also see how such bleed would be more disruptive without the serifs and the serif fonts would then be preferable.
With modern printers (or screen displays for that matter) such concerns would be as obsolete as the concerns that the serifs turn into smudges on low resolution screens.
The traditional rationale I come across is that serifs "lead the eye," but I have no idea if there's any real research about that. There's probably some truth to broadly stereotyping sans-serif fonts as generally more legible and serif fonts as generally more readable -- but I'm sure there's a myriad of exceptions. (Like, uh, Myriad, a sans-serif explicitly designed to be good for body text.)
So if there was any technological reason for them, it was either due to the stone carving techniques, or more likely to the limitations of writing with a wide brush, because the stone was carved after the letters had been painted with a wide brush, to guide the carving.
After the Imperial Rome, the serifs have continued to be used when writing on different supports mainly due to tradition.
The serifs are not the only difference between serif and sans-serif typefaces, the second difference is that the sans-serif letters are drawn with lines of uniform width, while the serif letters are drawn with a combination of thick lines and thin lines.
There are some modern sans-serif typefaces, like Optima and many others inspired by it, which are intermediate between classic serif and sans-serif typefaces, by lacking serifs but using variable-width lines, like the serif typefaces.
Even if the serif fonts are the traditional fonts, used almost exclusively until the 19th century, when the sans-serif fonts became popular for certain uses (e.g. for titles, for advertising or for newspapers printed on cheap paper) there are good reasons to use them besides the tradition.
Their 2 extra features, serifs and variable-width lines, make the letters more distinctive, less similar to each other, and in the opinion of many people, more beautiful.
Because of that, when rendered at very high resolutions, most people consider the serif typefaces more legible, even if there are also younger people, who have read few books on paper, but who have been accustomed with reading sans-serif typefaces on low-resolution displays, so they may prefer the sans-serif typefaces.
As another poster has already said, the advantages of serif typefaces are achieved only at high resolutions, i.e. preferably on 4k displays or better and when not using stupid dpi scaling, but actually using the high resolution for rendering. On the many garbage laptop displays with low resolutions, the sans-serif typefaces are almost always better.
Because of that, even if I use frequently sans-serif typefaces, I use only non-traditional sans-serif typefaces with variable-width lines, e.g. Optima Nova, Palatino Sans or Trajan Sans.
However, such typefaces with variable-width lines also need high-resolution displays to be useful. On displays with less than 4k resolution, their appearance at normal text sizes is degraded.