Their publishers actually have asked them to write under another name so their readers don't get flummoxed when during the crossover. Shows how much faith publishers have in their audience
Yes, it's really sad => authors are forced to stick to their genre instead of using a well-known name to introduce their audience into a new genre. Publishers don't see the chance.
Though some authors do this on purpose, to seperate their genres => Eleanor Alice Burford Hibbert wrote under 3 pseudonyms: Victoria Holt, Jean Plaidy, Philippa Carr.
Even Stephen King did that - he wanted to go away from the horror genre and write a plain fantasy novel: Richard Bachman. Wonder, why he decided to lift his anonymity later on and publish the book under his real name again. Maybe a "testing balloon"?
Ruth Rendell => Barbara Vine
Agatha Christie => Mary Westmacott, writing romance novels. Wish, I knew why she did that. Fearing an angry audience?
I think, it's dreadful, if an author is forced to do that - it's ok, if she/he wants to be free of the imago she/he has created.