When writers write about why they need publishers, they usually mention editing, marketing & advances. I imagine for many people marketing is not very relevant. Either the publishers will not do much of it anyway or the author has access to an audience himself. Advances are also (I imagine) not that important to many authors. Maybe some need the commitment as part of their process but purely as a way of financing, I don't see an insurmountable requirement that this be bundled with the other things they do. Most authors are not going to make money anyway so a small chunk now or a slightly larger trickle later doesn't matter much either way.
Is there a thriving industry of editors for hire? People who will take raw text and turn it into books?
What's the state of this ecosystem today?