Not all mail readers allow the user to do this easily without the actual address. This should give you an address to which you can mail a personal note. While this does contribute to the volume on PB, it is also a part of the community that we have built. The line between personal and group mail will be different for everyone. Although a message is short, it can cause a volume problem because of the header and because some members have mail quotas.
People sometimes do become mysteriously unsubscribed.
It is generally not a conspiracy, but just some computer glitch.