I recently finished reading Jean Auel's THE LAND OF PAINTED CAVES, which continues the story of Cave Wonder Woman Ayla and her Hunk Muffin Mate. 755 pages. 300 could've been edited out and done the book no harm whatsoever, in my opinion.
The core problem? Failure to focus. Storytelling is a lovely pastime, but it cannot amble down every last tangential path. Some novelists seem to enjoy rabbiting away down this side route or that narrow opening into who-knows-where.
Not my thing. I'm still working on the first draft of PEACEWEAVER, my 974 Wales romance, and my biggest challenge is to stay on target. Stay focused. Tell the story I'm meant to tell and not follow these characters down too many cattle-paths. It's tempting. I know. I've been there. My books are better when I can dwell on one conflict, one main plot, one set of characters, and not wander all over the landscape, attractive as that is.