I am kind of tired that any time a yuri ends and people expect more development everyone assumes the manga was axed, when most works on yurihime are 2-4-6 volumes.In various cases the “it was axed” (or “yuri is always axed”) allegation are mostly by people dissatisfied with the development and ending of a work, because again, most works on yurihime are short, yuri manga on seinen-shonen magazines are the long ones (which prove they are popular) but also, most of the time the length of a manga is discussed before serialization, sometimes its fixed, sometimes (when the author is popular) its free length, and yes sometimes they are axed but for what I have seen, authors don’t shy away from saying their manga got axed
It's not about an arbitrary number of volumes. It's about abrupt endings that no one saw coming, which signifies either poor planning on the author's part, or being cancelled prematurely. Usui Shio is not an inexperienced author. If they had planned for this series to end with 3 volumes, the manga would have had different pacing, and we would have seen the ending coming some chapters ago. Authors typically don't straight up say that they're being axed for failing to meet sales expectation, at least not right away, unless they want to burn bridges with their current publisher. You either read between the lines ("I'm sorry for letting readers down") or hear they mention it in passing years later. In this case, the fact Usui Shio didn't bother to promote this month's chapter on their X, when they always did it before, speaks volume.