Answer:
   
   Because such terms are inappropriate, and usually reflect a lack of
   knowledge about the group in question:
     * "Ultra-Orthodox". This term, when used properly, refers to the
       most carefully and detailed observant among the Orthodox, and who
       go to great lengths to keep away from most of Western culture. It
       arose as a reaction to the "Neologue" movement in 19th century
       Hungary, an extremely limp attempt at Reform (today they'd be
       called modern Orthodox, but such fine gradations didn't exist
       then).
       In practice, the term is usually used as a disparaging synonym for
       Orthodox or Chassidic. What passes for an unremarkable level of
       observance is inaccurately elevated into a form of "fanaticism".
       Many people outside the Orthodox community mistakenly identify
       those who wear Chassidic garb (long black coats, earlocks for men,
       wigs/kerchiefs for women) as "ultra-Orthodox." In fact, the
       Chassidic groups are no more or less observant than other Orthodox
       groups who do not dress so distinctively.
       The term "Chareidi" (literally: "trembling" as in "trembling in
       awe of HaKadosh Baruch Hu (the Holy One Praised by he).") tends to
       refer to the same people as described by "Ultra-Orthodox" but is
       more acceptable. It hasn't caught on in the U.S. yet.
     * "Reformed Judaism". The correct term for the Liberal/Progressive
       Branch of Judaism is "Reform Judaism", not "ReformED Judaism".
       "Reformed" implies that the adherents used to be Jews, but they
       learned and are now something else (e.g., early Christians were
       "Reformed" Jews). "Reform", on the other hand, indicates a belief
       in the ability to change (i.e., "Reform") the practices while
       still remaining Jews.
     * "Humanist Judaism". The correct term for Rabbi Sherwin Wine's
       movement is "Humanistic Judaism", not "Humanist Judaism".
       "Humanist", similar to "Buddhist", designates an adherent of a
       specific non-Jewish religion. "Humanistic Judaism" is a
       non-theistic branch of Judaism, based on a humanistic
       interpretation and application of Jewish traditions.