long? If you look at http://www.ams.org/notices/201410/rnoti-p1268.pdf (google “AMS notices backlogs” for other years), few journals beat that for papers, and many go way over that.

And yes, a short letter is different, but they might have a backlog of other letters to publish, may not want to limit the amount of letters per issue, and, for all I know, that June/July issue might have gone to print in May.

Even if the editors worked at infinite speed, in the end, this still is a paper journal with its limitation on number of pages, ratio of articles to reviews to letters, etc.