What's wrong with a passive champion?

Riot reworked Sona and nerfed Janna's damages for mid lane because they were too passive. But what's wrong with that? They will probably be less cancer than the interactive champions cough Yasuo cough and they wouldn't be much of a problem. While they are in good spots right now, my question is why do you need to make every champion interactive. I actually think a very passive champion would be a pretty cool idea. Pretty boring to play against but at least it's something.