Janeway is a canon character with 7 TV seasons of episodes and character exploration.
That`s the problem, there is little left to learn about her.
It would be very difficult for a non - canon character introduced in the novels to EVER have the story potential that she does.
I see it completely different. There was/is little story potential left for her. Even her relationship with Chakotay could be seen as just a rehash of the Crusher/Picard thing in TNG. A new character has a lot more story potential, exactly because she doesn't have the burden of seven years of canon to limit the authors in what they can do with her.
As much as the fleet exploration concept was interesting, in practice it had to be a bear for the author to keep track of and organize. There are literally dozens of minor characters in that fleet that would have been difficult for any new author to depict properly and would have sent most readers to Memory Beta just so that they can remember who Lieutenant Wehardlyknewyee was.
Wow, am I the only one reading this as somewhat insulting to both the authors and readers? You're basically implying that they have to keep it simple because neither the authors nor the readers are able to handle a couple of new characters.

and now we can go back to the main characters - which is why we bought the book in the first place.
Speak for yourself.