@vaartis He did finish PS quite nicely, so it's not like there's no precedent.
I noticed a pattern, though. Sometimes even very good authors just can't quite stick the ending, especially on big, ongoing stories. It may be a matter of author's emotional attachment. Noboby wants to just leave the world and characters they spent so much time and health creating.
*) araki syndrome, named after Hirohiko Araki, creator of JoJo Bizarre Adventure, known for the fact that as time goes on he got worse and worse at drawing dogs.