Why?

I sometimes read a blog that I think is quite fantastic. Fantastic because it inspires me in many ways, both personally and creatively. It teaches me not to take anything for granted and it teaches me to try new things.
The person who writes this blog writes it because it's an outlet for her, because she doesn't mind sharing. She doesn't write it to become the most read blog in Denmark, in fact, I don't even think she cares who reads it or not. I think she appreciates the people who reads it, but she would be just as happy if nobody read it.
Anyways, lately there has been another blogger out there who continues to leave nasty, vile, evil and hurtful comment on said blog. And I just don't understand it. What would anyone gain from that? Is it envy that leads someone to do such things? Is it hatred? Or is it simply that said person is mentally ill and we should in fact feel sorry for her/him?
I don't get it. Life is too short to hate other people and I know that my life and time is too valuable to be spent on negative things.
Sometimes it's better to not say anything if you can't say anything nice.
That being said, I hope said blogger will seek help and maybe one day look back and be truly ashamed.