The complaint isn't that, "We hate sexy women." The complaint is that, in a game with already heavily stylized, unrealistic characters (Find me men with the exact same proportions as Mundo, Singed and Yorick.) most of our female champs are similarly built, cookie-cutter characters when it comes to looks. In general, we have less female champs, but all the ones that fit the "adult human female" description are thin waisted, busty and generally considered attractive.
It doesn't HAVE to be this way. Is there honestly anything truly wrong with it? No. But there are plenty of players, such as myself, who would like their fantasy game characters to be a bit more... Fantastical. Seeing so many characters with that same ideal body gets dull. We only have ONE non-humanoid female champion without any human traits (Anivia.) For male characters, we have plenty of animals and monsters, and even in the humanoid characters, the range of variety is much greater. Even looking solely at the "adult human males" many of them show clear differences. (Garen vs Twisted Fate vs Graves vs Jarvan) Sadly, our female champs don't share quite that trait, and some people are disappointed that we aren't getting more Yordles, more creatures and monsters. Even when it's a basic human character, not every single woman has to have the same build. Obviously the men in this game don't, so why do the women have to be boring and samey?
Of course, this is all a matter of opinion. Some people are just fine with it. There are plenty of people in the playerbase, however, who are not and would like Riot to take notice of what they would like to see in the game.