It seems to me these people think webnovels are your average closed volume novel's chapters sliced and published in pieces in internet... and no, it isn't. The model is similiar to webtoons, where a novel has a start, an outline, but doens't necessarily has a given number of chapters to end.
I wonder how shocked they would be with that chinese wuxia and xuanxia novels with more than 3k chapters...
And yes, it doesn't make sense for you to spend twice in the same thing, unless you're a hardcore fan and wants the thing printed for you to sleep hugging it or if the series is finished and the author is celebrating inserting some extra exclusive content. I'll be honest I'm very satisfied publishing it online and drawing illustrations just for the funs.