Farecast and subsequent Bing Travel employee here: I had already moved on by the time the decision was made to discontinue the fare prediction service but I think it was mostly due to the amount of work it took to maintain a high accuracy rate and the large amounts of data we had to ingest to do so. Over time, there were less people from the original team working on it and the data options were limited (ITA was a major source of data) so it was discontinued. Glad to see we were ahead of our time!