It goes more to the underlying psychology of brand association. We humans tend to associate things that occur together, such that if you see two stimuli togeth

It goes more to the underlying psychology of brand association. We humans tend to associate things that occur together, such that if you see two stimuli together often, then seeing one will evoke the other even when it is not present. Brands want to be associated with positive emotions. For example, Proctor and Gamble wants you to feel happy and think of fresh smelling things when you hear or read the word “Tide”. Placing ads next to content that evokes strong negative emotions, does the opposite of this. Controversy is strongly associated with negative emotions. Thus brands do not want to pay to appear next to controversial content.