This article talks about a phenomenon that has been occuring since February 2010.
If you google the names listed here there are various and sundry reasons for the
resignations. The article itself does at the end express concern that there are so many
and that several are sudden and without explanation. One chief resigned within a few
years of the availability of his pension! The article also expresses an explanation
at the end--that possibly these chief have been aprised of that they might
have to arrest and imprison private citizens in the near future. . . who knows. There is
also a link about CEO's resigning. I also recall a few years ago about the mysterious
deaths of several bacteriology experts.
Maybe someone has already posted this--sorry if that is so.