Simply looking up the site's web traffic implies that approximately 70.4k people visit Scribblehub every month; it'd be foolish to assume that less than half of those people are readers.
You're making my point, again.
First, you're assuming those are all people. Second, 70,000 is a small pool. Not as small as some (as Cardon points out above), but quite small. Even if they're all people (not), and even if they're all registered (not), one would reasonably expect at most 1-3% to skim a fiction's synopsis as it passes through the "Updates" scroll. Of those, one would expect at most 1-3% to skim the first chapter and click "Follow" or "To Read."
I'd expect a native, organically grown audience of at most 30 followers and/or declared readers. to have accumulated over the course of posting a complete book (or in the more common scenario of webnovel never-ending-stories, say a hundred chapters).
Incidentally, 70,000 (if reliable, which it isn't) is somewhat comparable to that little website with two 'R's. Which advertises its membership rolls. That little website has around 80,000 registered members, give or take. Over the past five years. Most of which are presently inactive. Web traffic sites are completely useless for determining activity versus lapsed participation. Web stats don't distinguish between registered members and
transients, that is,
readers who come in from elsewhere, typically on a favorite/bookmark to one webnovel, on a link that they got from somewhere else. Those people typically don't even see SH's home page. Let alone poke around in search of something new.
Over the past couple months, I've posted a complete novel at that other site with two 'R's. It has three (!!!) unsolicited reviews, nearly 100 comments, around 10 ratings (not including myself), and 26 followers. I consider it to be vastly successful. Before I started posting, I projected that I should consider it a success if I got 30 followers (based on the size of its registered member pool), and I'm on track to hit that goal over the next week or so.