Because xbanner is used by xdm, I guess.
maybe xdm should be put into a separate package?

I think it would be good to split xdm config files and the like
off from the main X package, so that people can still install the
base X stuff on a small system without having to pull in all the
stuff that's just there to make it look pretty and isn't necessary
for functionality.

 Better would be a general revision in packaging to split 'pretty
config files' away from everything else. For things like XDM, I'd
suggest that there be a 'basic' set of config files in the core
package, and another set of optional pretty config files. If the
pretty config files are installed the basic ones can notice and
include them; only the pretty config files would require things
like xbanner et al.

 This may well be too complicated for RedHat to find worthwhile.

Thank you for your suggestion. It will be considered for the next
release of Red Hat Linux.