A common piece of advice often repeated for fiction writing: when you finish your novel, leave it untouched for a few months (e.g. six months). When you return to read it again with a fresh eye, you'll spot all the clunky passages, clichés, and poorly written characters you didn't spot when you were immersed in the writing. The space of a few months gives you a more critical eye.
That's the advice. Whether writers actually heed it I don't know. (A pause of some months might feel too long for some writers itching to be published.)
It’s like bands that spend years polishing their sound, but never actually write any songs.
I'd actually be interested to read some of those - I wish there was some kind of standard media form for that. E.g. I enjoyed reading the Eclipse Phase sourcebooks much more than actually playing the game. And while I didn't actually enjoy Christopher Priest's The Islanders, I liked the idea of the form.
Source: have written several unreadable novels.
He talked about how one of his books basically sat on the shelf for ages (possibly a year), he just couldn't get the idea to work, until one day he came back to it and figured it out. People massively underestimate how much work it takes to turn an idea for a story into a working novel with a coherent plot and characters.
In sci-fi and fantasy I think this is particularly obvious. There's a lot of sci-fi that has an interesting idea or concept at it's heart, but the actual story just falls flat. I think it's why short stories are often a better format for sci-fi ideas.
Similarly I've encountered a lot of fantasy that was all about world-building but where the book itself just went nowhere. World building is kind of easy compared to actually writing a novel with a compelling story. It seems to be common for aspiring fantasy authors to spend years doing the former and never getting round to the latter.