Why create such a complex cipher?

[BessAgritianin]

..... 
If all you are doing is hiding information about botany, why do you need to go to such lengths as the scribes did? Iirc both Alan Turing and the guy who cracked the Japanese code in WW2 worked on the manuscript (and failed), so, if you're a 14th century botanist who wants to hid information about your plants, why do you need a cipher that is more difficult to crack than the Germans and Japanese used in a world war? 

  It is definitely not all about botany, but about healing, making of the medicines, and explaining processes. This information was considered highly secret in the middle ages and passed usually from father to son, or from teacher to a worthy pupil.
  Do not underestimate the creativity of the ancient wise men. I know of at least two other cyphered ancient documents, which without knowledge what is the content behind, you cannot read them at all.
  One of them is the Psalms from the Bible. If I ask nowadays why should the "Psalms" be cyphered and wonder - the 14 -century Christian will know it immediately- because of the Osman conquerors, being Islamists chased after Christianity. 
Many monks started secret writings of the Sacred texts to avoid the burning of their documents and their monasteries.
   Maybe the cipher-man of VM was afraid of the Inquisition (with all these naked figures), or who knows?
BR