I'm rewriting stuff I've written before in other posts, but in essence there is an implied promise that if a reader buys into the series that the author will make a good faith effort to finish the series. This isn't always possible for various reasons and this is ok. Certainly, it wasn't required for Robert Jordan to spend the last of his life outlining the WOT series, but I'm certainly glad he did. But when an author really doesn't appear to make an effort to finish a series then yeah that is an insult to the fan, because it broke the trust that the fan placed in the author to make an effort to finish a series.
In the days before kindle, books might have blurbs on the cover or maybe in an advertisement in the back that might say something like "the first in an exciting new trilogy by 1980's fantasy author." Why would any reader buy the first book in a trilogy if there was never going to be a third book? The answer is that the reader wouldn't. There is always an implied promise that there will be an effort to finish the trilogy or else fans wouldn't buy trilogies until all the works are written.
Fraud, as defined by the first internet definition from google is: "wrongful...deception intended to result in financial or personal gain." In the case of the author not finishing a series just because, the wrongful deception was that the author would make an attempt to finish the series and the financial gain was the sale of the book. I excluded the legal bits of the definition, because I have no interest in typing a long legal analysis. If an author commits a fraud, in common parlance, on the fan then yeah that's an insult.
Who said anything about severe physical or mental anguish?
I do believe an author intends to finish the series he or she has planned.. However problems do arise that prevents it from happening, or sometime as in "Game of Thrones," a trilogy becomes extended to several more books. I think a problem arises when an author promises too much
to his or her readers. It's great to promise a 20 book series, but is it realistic? There are a lot of factors that decide if this becomes a reality or not, putting aside just what life throws at anyone, but the ability/desire of the author to devote the next twenty or so years to finish the series... If Martin had strictly devoted his writing time to the series itself, "Game of Thrones" would have been finished long ago... But while he written and published several books about the world it is in the last few years, the series itself remains undone. While it seems like Jim is taking longer between books and he has had a lot of personal things in his life, he still has managed to begin a new series with a pretty long novel.. He throws a crumb our way once in a while with a short story set in the Dresdenverse, but that hardly satisfies..
No, he isn't our bitch, and no, he isn't obligated to finish this or any other series. However he may owe it to himself as well as his fans if Harry continues to find a cooler and cooler place in the back of the stove of his mind, to perhaps realistically rethink the scope of the story... One last thought, it has been my experience that some wait and anticipation of book, movie, or television series can be good, too long and it usually backfires and disappoints...