Comparing the cost of a webnovel to a book on Amazon will vary. As has been pointed out, one webnovel is more comparable to an entire series. You can find box sets for pretty much every genre. Sets that have anywhere from 2+-12+ novels inside them. If you know where to look, there are tons of box sets priced at $0.99 USD. Their quality is comparable—or better—than those here for the most part, and I haven’t run into any yet that contain high levels of filler. They exist, I’m sure, but are not the majority.
Amazon takes a 30% cut—provided the price of the book is between $2.99–$9.99. As for WN losing the money from ads, we've been told many times that they make next to nothing on the ads, so I don’t know why no ads would be a deterrent for them.
I joined right after they shuttered the subscription service. Even so, I would have become a paying customer if the cost for the novels was reasonable to me. Yes, I know you get longer books, more comparable to series, but I can find the same lengths act Amazon, via box sets, for a lot cheaper. After watching how the company does things—customer service, etc.—I will not likely ever become a paying customer even though that means reading significantly less.
Focusing on the customers with bigger wallets is a valid strategy, but if they started out by focusing on attracting and retaining free or low spending customers, it’s to be expected that some will complain. Anyhow, I’ve learned a lot about business here, for which I am grateful. :)