Why create such a complex cipher?

[oshfdk]

Voynich manuscript doesn't have to be a complex cipher.

See for example:
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It certainly isn't rocket science but if you don't know the source book then you are practically hopeless.

For me the Voynich Manuscript may be something like book cipher - a colllection of numbers pointing to some words on the list. It is extremely hard to break if for example "herb" is 97, "flower" is 520 and "leaf" is 343

If this was the case, with no extra tricks, I suspect VMS riddle would be extremely easy to solve, much easier than Rohonc. There are hundreds of labels in VMS, if, say, "otarly" consistently meant "water" and "okaldy" stood for "hot" (both examples are made up), there would have been multiple convincing reading already. I'm almost absolutely sure that if this is a cipher, it's of a one-to-many type, with several possible ways of representing a single plaintext word.