This is because of the stereotype that has now been created for Reddit. Because of all the negativity and media blitz about the negativity surrounding Reddit, people automatically assume that Reddit is only about the most heinous things that human society has to offer. There are some fantastic content/communities that depict the wonderful and redeeming qualities of our society (wonderful photography, creative writing prompts, etc) that only Reddit can offer, however it looks like people don't want to take the time to find this wonderful content on Reddit.
I came to Reddit as an unknown, and as such, when I discovered the site, I was ignorant about the negativity that surrounded this website. I came with an open mind, and to my surprise and amazement, I discovered some truly interesting, engaging, and helpful communities. Unless you are specifically looking for the negative and hateful communities, as a newcomer, Reddit makes it very hard to scope out these communities IMHO.