1) Because old people are cranky and stuck in their ways. A hatred of anime can be sourced to Imperialism, xenophobia, and/or racism, but general cartooning is just old fogey issues. Disney-styled gets either a hard pass or an excessive dislike just because of it being mainstream.
2) Because a lot of young artists who draw cartoons tend to have skipped the entire fundamentals stages and instead of drawing from the knowledge of life, they are stuck in drawing simple symbols because that's all they know. It's not hard to tell the difference between shortcuts and rules that are knowingly broken.