Manhwa are very mobile friendly, the language is simple, and most notably they are colorful, which attracts audiences and makes it quite accessible. Compare it to some of the more dense manga you might read where sometimes a panel requires a lot of pinching and zooming.
For sure though, as the article points out, there are a lot of amazing and intriguing stories in manga, which have better story density compared to the thinner, spread out stories in manhwa which are catering to an audience that just wants to keep scrolling. The artstyle too, I don't think we're going to see anything close to Junji Ito or Berserk style work in webtoon format anytime soon.
But anyway this trend of manhwa's popularity has been noticeable for several years now. The top entries on manga 'aggregator' sites have been manhwa as well.