Well, my books are edited by my editors -- Anne Lesley Groell at Bantam (US) and Jane Johnson and Joy Chamberlain at HarperCollins Voyager (UK). I do send them sections as I go along -- not individual chapters but sizeable chunks -- but the editing does not really begin until I deliver the finished novel. At which point they read the book and give me notes, and I revise. Then the manuscript goes to a copyeditor, who checks it for grammar, syntax, spelling, internal consistancy, and the like, and flags any mistakes. Which I then fix. Then the book goes to the typesetters, and I receive a set of galley proofs to check and correct. The typesetting process introduces new mistakes that have to be found and corrected.

All this takes time, obviously.

I have heard the same tales as you of writers who submit chapter one while still writing chapter two, but I could never work that way. I revise constantly as I go along, always honing and polishing. I may get a new idea while writing chapter fifty two which requires me to go back and change chapters three, nine, and twenty-one. If you lose the ability to do that, because the earlier chapters are already set in type before the later ones are finished, you're binding yourself in chains.