Why are the 5 megillos called megilla and not sefer like the other 19 books of Tanach?
It can’t be because they are short, because A) Sefer Daniel is just as short as Megillas Koheles. B) Trei Asar is a collection of short neviim so if short was an issue here they could have been put together in one sefer and called Sefer Chamsha. (agav why trei asar in aramaic?)
It can’t be because they are one-topic books, because Sefer Iyov is one-topic and is a sefer. The same could probably be said for Sefer Mishlei.
Any info would be appreciated.