The Voynich Manuscript is a cipher because...?

[-Job-]

It can be difficult to separate a cipher from a constructed language.

Maybe a better question would be, why is the Voynich Manuscript not a natural language?

It's really not better to phrase it that way. I want positive reasons for the Voynich manuscript being a cipher. If folks' beliefs truly boil down to, "it's a cipher because I don't think it's a language", then I think the whole side of cipher research on the VM has a serious problem.

I agree that it's important to list supporting features (which i did), my point is that ciphers and constructed languages overlap.

For example, the VM's internal word structure could be taken as evidence of a cipher or a constructed language, so it won't make it into the list of reasons why it's a cipher.

The line is clearer between a natural or artificial text.

Out of curiosity, what positive arguments do you have for believing the text is an unencoded natural language?