This guy from the source made a really good analysis of why people prefer watching Aqua get bullied. Worth a read

It's interesting considering how the main character being gaming trash plays into this. I remember people hated Umaru so much. Kazuma at least could star in an episode without any of his supports and it wasn't terrible. It helps that few of his mistakes were self-inflicted, being a slacker, and that once forced to by sheer plot he could get things done and be reliable. If Umaru didn't have any support she was a flop, her support was also more interesting to watch alone. Which I realize defeats the purpose of these shows. Gabriel I don't feel any empathy for at all. Her "angelic genius" being easily corrupted by playing healer in an MMO is not funny. It's a sad joke because it's too close to reality. Instead I feel empathy for the people that put up with her.