I've just watched this documentary and I'm still venting... I must get these vapors out of my system!
Why are people so credulous when it comes to classical music?
It's not limited to classical music. Why are people credulous? Well, for a great many reasons. In this case we have a confluence of several:
i) Bach's works have been analysed for hundreds of years, and little new information has emerged. That means it's hard for anyone to find anything new to say.
ii) its fits a nice contemporary narrative. Unquestionably, talented women have been repressed and marginalised throughout history, and only relatively recently have they received their deserved attention. This means that the potential rediscovery of another such women fits the scholastic zeitgeist, and so attracts the attention above its actual scholarly value. Twenty years ago we'd be asking if Bach's second marriage meant he was secretly gay. So it goes.
iii) the continued fascination with postmodernism in all facets of the arts mean that strong factual evidence is not actually a requirement, and people can be published on the basis of "analysis of penmanship" - a pseudoscience that makes phrenology look credible.
If you're into Classical Music and Bach in particular, read on.