Hey, that's not a fair question. Who knows why government sites link _anywhere_?
The U.S. Department of the Interior has not one but two humongous sites, each with pages for (almost) every National Park. Are they cross-linked? And why not? Don't ask, nobody will admit the real answer. (After all, neither one has a page on Roswell.)
Bureaucratic turf-warlords. Bah.