How many people penned the main Voynichese text?

[oshfdk]

Again, this is possible. But why would this explanation be preferred over the usual assumption in manuscript descriptions that different hands = different people?

The usual assumption works when scribes use familiar scripts, that they have practiced writing for years. It's highly unlikely that the established well learned handwriting of a professional scribe will noticeably change over the course of a single manuscript, hence if there is a change in handwriting, usually another scribe is assumed.

However, when writing in a new unfamiliar script, it's expected that the handwriting will evolve and writing habits change as the hand adapts to the script. Interestingly, if I remember correctly the work of Lisa Fagin Davis, the most striking difference between the hands was in the execution of the gallows characters, the very characters that are highly specific to the Voynich script.