That's an interesting perspective. In my mind, though, the successful jokes (L-Block, Missingno, WCC) win not just because they're funny, but because they also remind people of something they like - Tetris, Pokemon, Portal. Hitler doesn't tend to generate a lot of positivity like that, even as an effective villain - and he certainly is a powerful villain. I think there are enough people who just don't find this one funny, whether they're offended by it or not.
Well, I guess Hitler isn't really "funny", but you get what I mean. Funny like novelty funny not funny like "haha that Hitler is a funny guy!" funny.