I mean, really, why would it be encrypted?

[Mark Knowles]

Why write a whole manuscript pretending to be something it is not? With regard to most of the illustrations, one could assume at first glance that the content contains little that would have to be kept secret. Unless, for example, it is a manuscript for the production of Theriac or something like that (secret herbal ingredients, secret manufacturing process, recipes). In any case, the encryption of such a large amount of text requires a high degree of motivation. The vanity of the author(s) would certainly have been satisfied with a few lines.

René linked to a manuscript of medical recipes (in Latin) that was written entirely in a substitution cipher.

And let's not forget Giovanni Fontana. Why did he write his manuscript in cipher?