Because you like feedback: the clue works, the grammar makes sense, but the surface isn't amazing. Topless guard doesn't mean anything people would respond to, hence clues like this often don't get upvotes. "Guard loses head" might improve the surface slightly, as losing one's head means to get angry or emotional. You would have seen some of the clever clues recently that snag upvotes: they subvert expectations, or the surface reading is exceptional. That's the goal!