I've heard that a huge percentage of people on the Internet are lurkers and that those posting and commenting are in the minority. Not sure if that's still true in the age of smartphones. I'll often leave comments on YT vids and such if they were interesting or helpful, but I would say a lot of people I know probably wouldn't do the same. I would probably not do the equivalent at an in-person talk, so that's an interesting contrast to think about.