Why does every distribution upgrade remove xscreensaver?

[Adam Funk]

I've been using xscreensaver for a few years, especially since the
gnome-screensaver went all boring.  Every distribution upgrade on
several machines for the past 2 (at least, but I think more) times has
removed xscreensaver even though it was manually installed, so I have
to reinstall it after the upgrade.  Is there any good reason for that?
Any way to prevent it?

Thanks,
Adam