Yeah, it's called real life I suppose. We just have to accept that writers who post on a chapter by chapter basis will show a high level of degradation. Most of these writers seem to start when they are young when life's responsibilities and demands are light, then along come relationships, work, family, mortgages, expanding interests, expanding responsibilities and so on. Of course, it isn't just the young, people start to write at older ages as well, often in response to life changing events. Jeffrey Archer started writing in mid-life after his businesses went criminally belly up and he was left with no reputation and no way for gainful employment as he could see it. Amis the senior I believe started writing as a paliative after a medical diagnosis gave him less than a year to live, erroneously as it happens.
Some writers are very prolific, but never seem to be able to finish anything, others simply give up at the first hint of a hostile review, others just seem to lose their way. In short there are myriad reasons, most of which the reader never hears, for the death of a story which is truly disappointing when the story is of very high calibre, like Kandric, the Scrolls, Sentenced to Life, Songspell and far too many more.