>>16258811Because Unova OU was bloated with Fighting- and Steel-types, GottaGoFast was in full effect, and Dark STAB was shittier at that time and in that tier that it ever has been. Meanwhile, Ubers was full of Psychic and (technically) Ghost-types begging for a Sucker Punch to the face, while also having relatively few Steel types to wall the endless Dragons and a near-total lack of Fighting types.
It actually makes perfect sense, given what each tier looked like. The Mach Punch/Close Combat spam that kept Bisharp out of OU was entirely impractical in Ubers.
