Perhaps one reason is the sheer volume of material available. For the people who refuse to wade through the mass of good advice that's out there, I have distilled it down to one page of the guidelines that I followed when I wrote my first novel. My advice is to rewrite your work until it can pass these seven basic tests before submitting it anywhere. If you have plenty of advice sources already and don't need more, now would be a good time to stop reading. John Ross' Seven Suggestions for Writing a Novel 1.
Some authors claim they just start writing and see what pops out.
If they do this and are successful, more power to them. I cannot imagine following this path and ending up with something I liked. Don't start writing until you have an outline that you really like. Publisher's Weekly reduces preview descriptions of new books to ONE sentence. You should be able to do this with your book, also.