Getting a book printed isn't super-easy. I doubt somebody would bring the content of a typical webnovel to a publisher and they'd just print it without having it go through extensive passes of feedback and editing to the point that by the end of it, it'd barely resemble the thing it was originally stolen from. The only instances in which I've seen web-stories just go to print with very little editing, it was because the original web version was already popular, which convinced the publisher it was fine as it was, had a guaranteed fanbase, and didn't need a lot of work (common with novels that started as popular fanworks like 50 Shades of Gray). Most of the time, if somebody publishes a novel online, it's because it's too niche for a print audience, or because the writer's work is still a bit rough and not yet up to standard to be published, so I think there are pretty low odds somebody would both want to steal a webnovel, and then that it would also get picked up by a publisher.
Editors and agents aren't stupid. If somebody suddenly comes out of nowhere with no traceable writing experience with a fantastic, fully-formed complete novel, but then doesn't seem to even know where to start on writing subsequent drafts, they're going to be suspicious. They'll probably also be suspicious if a person's submission is vastly different from and far higher quality than any past examples of their writing found online. It's a really obvious red flag.
The only companies that'll just print a book for you, no questions asked, tend to be vanity publishers, where the writer pays the company to publish and print their work (rather than the publisher paying the writer for content they can publish, print and sell), and even they would probably use plagiarism detection software similar to what teachers use for essays, to run a basic check, because nobody wants to get a Cease and Desist after spending thousands on a print run and then having a ton of unsellable stock and a big scandal on top.