Or more to the point: Why do writers do this to themselves? Consider this question for a (relatively brief) moment, given that if you are a writer, you already know the answer - and if you're not, well, your interest is already waning.
Writers don't chuck out novels in weeks (well, some do, but those don't involve anything called quality). The usual timetable features long-game words such as months (at least the duration of your typical pregnancy or tireless Major League Baseball season); years (anything from enough time to watch a rookie Congressman turn into a veteran scumbag, or for Microsoft to end support for its second-most-recent iteration of Windows); or decades (think: declining hairlines, sagging bellies, or every time the Boy Scouts of America changes its policy about gay members).
In those long-game windows, we beat ourselves against figurative brick walls working out story conundrums, character journeys, and the nagging feeling that we could be doing something more productive to change the world. We work in solitary confinement as we make up shit that might someday find resonance with the tiniest sliver of the population, if we're lucky. And then we revise, because making up shit the first time wasn't enjoyable enough. And then, upon deciding we have an acceptable story, we move into the editing phase, which is about as thrilling as watching the House Finance subcommittee live on CSPAN2. Except for the sliver among us who are established, successful authors with a loyal fan base, our odds for publication through the traditional route offers slim hope at best and no reason whatsoever for quitting the day job. (After all, aren't pensions the whole purpose for living past 65?)
So why in the hootenanny do we put ourselves through this?
I'm going with a one-word answer: Self-preservation. (OK, so it's one hyphenated word.)
Novelists walk this earth weighted down by the burden of an attention-starved imagination. From time to time (or perhaps every day just before lunch), the Imagination regales us with stories that it DEMANDS we put to paper. Over time, failure to meet these demands risks facing an imagination as impatient as the 73rd guy in line at the DMW. Unless that line starts moving, there's going to be grumbling. Before long, violence will ensue. In this sense, novelists are frail beings who prefer to cow-tow to the grumbling for the mere price of maintaining serenity of mind and spirit.
We can write these stories or .... or we'll be left few options but to consume Fritos and binge Netflix until we realize that the series we're watching is based on a great idea for a novel we had 22 years ago. Which of course means it's time for a nuisance lawsuit. But only if the series is REALLY successful.