Why do we think the Voynich manuscript has multiple scribes?

[oshfdk]

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?

Increasing the number of people makes it less likely that the whole manuscript is the result of an ill mind in a particular individual. I can imagine someone suffering from a debilitating neural problem feeling compelled to keep writing/drawing even if they are no longer capable of expressing their thought coherently. If we are talking about 2 or more people, this explanation doesn't work. 

I think this famous set of self portraits of William Utermohlen documenting the progress of his Alzheimer’s disease shows some resemblance to the way human figures deform in the Voynich manuscript. Unfortunately, I think most arguments about the number of hands in the manuscript might not work if we are dealing with a person whose skills vary greatly between bad days and good days. On the other hand, this could explain the nasty paint job, if this was the last step in the process of creating this book, the author's motor and/or mental skills could have degraded even more.