I'm of the opinion that it's not supposed to make sense. I think it's a sample: a demo herbal void of any valuable content. Its purpose is to showcase the abilities of the author/illustrator and nothing more.
According to [0], "A long succession of (actually pretty good) past statistical studies has revealed that Voynichese has an abundance of mechanisms that give it internal structure, not only in terms of letter adjacency and within words generally, but also within lines, paragraphs, and pages."
Whatever process generated that structure, it seems like it required more work than is necessary to achieve the aim you suggest the writer(s) had.
[0] https://ciphermysteries.com/2016/01/21/voynich-statistics-an...
https://skeptics.stackexchange.com/questions/6085/has-it-bee...
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.