What Pearl-chan said, I think you're really underestimating Scribbly's potential tbh.
Like... For now most users are people that come from NU, but that won't be the case forever. Scribbly has an official discord while NU hasn't because Tony-chan believes Scribbly has more potential than NU actually.
And the fact Scribbly has an active developer constantly improving the site is a considerable upside when compared to most competitors out there.
Scribbly's target audience isn't solely of anime fans that like novels and want to read, it's a site for posting any sort of Webnovels one wants (as long as it doesn't break the site's policies), it will surely have more and more people writing different genres than what you see in NU as the site grows~
To give you a notion, if you search
Scribbly in Alexa, you'll see that just 3 months ago it was ranked at #80000 in internet trafic, and now it's at #60000, that's a huge growth in a very short period of time. By comparison,
RoyalRoad went from #13500 to #11300 in the same period of time. Both sites are still growing, but Scribbly is doing it a lot faster... Which is normal, when considering it is a pretty new site and stuff, I just don't think it will stop any time soon~ (and on a side note, the average amount of time a visitor spends in Scribbly is 12min, while in RoyalRoad it's 10min, so Scribbly is making people spend more time on it in average)