Well, I was approached to pitch a series to be a Featured one. Personally speaking, I wasn't what they were looking for but they told me "If your series becomes popular, we'll come back to you! We encourage you to publish it on Canvas!". However I believe they didn't actually care about my pitch since they first mistook the name of the Series for 2 another ones I worked on but never mentioned to them, as well for the fact they ignored the main focus of the series and only cared that "Comedies aren't really popular on the platform" (But my story was not a comedy, it was a Urban Fantasy
)
Back then, they were launching Webtoon Spanish so they wanted "series oriented to Gen Z to appeal the latinamerican cultures" So I based my story on Argentina, focused on a teenager girl who was going through the phase of discovering her identity, what she wanted to do once she finished high-school, working part-time for her brother at his Pizzería and on top of that, supernatural creatures (From latinamerican mythology) living among the human society. Basically I wanted to make a drama involving leaving the comfort bubble of childhood to enter adulthood, and the crash of said worlds and perspective. 
Usually, webcomic making specially on Webtoon has a long period of backlog making so you won't have to do weekly episodes of 40 panels with a short deadline. Usually, they work with artists and authors for nearly a year with preparation before starting publishing the series as I've seen some of Spanish authors that became Originals delaying their debuts at least twice. This is according to other people who became Featured authors, but obviously, if your series doesn't meet the criteria it can be cancelled at any time or become a 40 episode story at least, you're not only being paid by the amount of panels but by viewership if I recall correctly but these "plus"s are only added to the later episodes, not the first ones. Webtoon has this thing that they need each episode to end up in a cliffhanger and their formula it's always pretty much vanilla when it comes to plots when it's not an action/adventure/suspense story and yes, they stretch it a lot and fill in between.
A lot of Canvas Authors actually reject becoming Originals not only because they'll have to re-draw their series, simplify them, color them (Yes, grayscale or white & black webtoons are usually rejected) as well to modify the time pace of their story according to an editor but because they earn more money with Ad Revenue and their donation platforms than with what Webtoon would offer them on contracts. And of course, assistans/any additional help is payed solely by the author, be it colorists, background artists, secondary editors, letterist, etc.
I got contacted too to apply to be the artist for another of their pitched series but I rejected the work since even if they didn't provide me the name of the other author or the series, the plot alone was... too boring and vanilla to me, as well I already worked for a romance story so I didn't want to work for another one back then.
Right now I'm working on three different series, so I have my hands full, as well I like to have free time for myself be it to doodle my own stuff, make art for friends or simply taking naps. I'm not struggling in terms of money so that's also another reason.