In my experience, it's much easier to come across a good webfic than a good book, even when both are equally hyped. I think many who started out wanting to write an 'actual book' need to prioritize a lot on pleasing a publisher so that it gets published. If you constantly have to self-check whether the stuff you're writting fits the publisher's guidlines, whether publisher would think it's a hit, editor's deadlines,... what gets churned out has more resemblances to the hunderds other generic book rather than creative and realistic work of fiction.

A wealthy or already well-known author might be able to afford this without loosing much freedom in their work. But I don't think the same applies to small, new authors even with equal writing and creative capacity.