Why did Giovanni Fontana write his book in cipher?

[Mark Knowles]

Well, if we compare abstract theories of nature with technical drawings of engineering, we can compare the Voynich to Fontana.

Both the Voynich and Fontana's works are amazing, but they are not comparable.
Fontana is showing off his work to his contemporaries, advancing his knowledge and advancing his prestige within his guild and his profession, showing off to his patrons and developing his own ideas.
The Voynich is.... well, we still don't know what it is, but it isn't doing what Fontana did in the same way.

I suppose whether their works are comparable is just a question of perspective. My perspective is that it is fruitful to compare them.

I think what I was driving at was the question as to what we know about Fontana's motivations rather than what we might think his motivations were. What do we know about what Fontana wrote about his motivations? I haven't studied his work, but I wonder if he writes what he sees as the motivation or purpose of writing a specific text. I think what one might hypotheses that his motivations must have been is weaker than primary evidence of what he said his motives were or what others said that he told them his motives were.