Why did Giovanni Fontana write his book in cipher?

[Mark Knowles]

I think evidence is key. But my own hypothesis as to why Fontana and Voyauthor wrote their manuscripts in cipher is that:

1) They could.
2) It was so they could feel clever i.e. vanity.
3) It was a way of showing off their skills to friends and acquaintances.
4) It was of interest to them.
5) They wanted to keep the contents of their manuscript secret.

However one needs primary evidence to clarify Fontana's motivation. Here evidence is much better than hypothesis.