Why do people say Uggs are girls boots?

Because women started to buy them, and UGG started to create their designs for them like the bailey button and the new kimono line. I mean, I have a pair (Classic tall chestnut) but I don't think that pink and green UGGs are for men. And also, most men don't wanna spend over 110$ on boots! The slippers I understand but boots? You can wear them all you want but not alot of guys in the US will follow your fashion statement... sorry :'(