For the same reason we have "futanari" instead of "hermaphrodite", "seifuku" instead of "school uniform", "yuri" instead of "lesbian", "gaijin" instead of "non-Asian chick"...need I go on?
Although actually, I need to change the tag. 'Twas a good attempt, Anonymous, but my dictionary lists 'aikou' as 「物事を愛し好むこと 例:釣愛好会」, which means it only applies to inanimate things or concepts (i.e. 平和を愛好する）so I'm gonna switch it to 'aijou' (相手にそそぐ愛の気持ち・深く愛する暖かな心) ^_^
