Why do we think the Voynich manuscript has multiple scribes?

[Jorge_Stolfi]

For me it's very obvious there there are at least 2 persons involved. Compare for example You are not allowed to view links. Register or Login to view. and f31r.

You mean these parags?
   
   

Frankly the handwritings don't look different to me.  There are differences in glyphs like r, n between the two pages, but there are the same differences within each page.  What detail specifically do you think stands out?

The lines on page You are not allowed to view links. Register or Login to view. are more straight and parallel, but that could be the result of something as trivial as the Scribe working on his scribal desk versus he working on the counter at Starbucks, rushing to meet the day's quota...

On the other hand, I cannot avoid noticing the water stain along the top edge of f31r, and how it partly washed out the text there.  Iron-gall ink?  Ha!...
 

On the other hand I wonder is this question about the number of scribes really helpful in solving the manuscript. What would it give us if we know for sure that it was made by 1,2 or 5 people?

The number of scribes makes no difference if one's "origin theory" assumes that the author and Scribe(s) were different persons, and that the Author alone understood the language/code.  

However, that issue is very important if, for instance, one assumes that the VMS was meant to be an "information transmission tool" between two or more people who knew the language/code and wrote it themselves.

By the way, I find it disconcerting that people dismiss the Chinese Theory or the Retracing Hypothesis as "hallucinations", but accept pacifically the idea that there was some Medieval society or cult that devised the Voynichese "code", created a totally original cosmology and medicine, and set out to write down that esoteric knowledge in an encrypted encyclopedia... 

All the best, --jorge