If it was written in Latin during an era where everyone could read Latin, it wouldn't be the same concept.
It would probably be a bad idea to juxtapose religious text with the borderline alchemical pictures in the manuscript. People are/were a superstitious lot. Also, you wouldn't want to risk angering the church. Aesthetically it would also be a bad fit, because this (probably?) isn't a Bible. For the type of content on display here, it probably wouldn't do to remind the client of Sin during the pitch.
> [why] produce such a large volume when several pages would have sufficed?
Here's a similar volume of pages with no meaning but to showcase the capability for presenting a particular type of content: https://www.squarespace.com/templates Only instead of Photography, Online Stores, Blogs the categories are Herbal, Astronomical, Balneological, etc.
> Why?
I think we can be fairly certain that whoever produced the Voynich Manuscript was at least a little hmmm... eccentric? We should probably be moderate about how much sense we expect to make from it.