The folks calling for Crockford to be disinvited weren't complaining about his talk quality, they were complaining about his behavior. And there really isn't much beyond what this blog post mentions that they are complaining about. One person cited a post of his from 9 years ago about weight loss as being evidence of him fat shaming. They also cited a GitHub comment from 4 years ago where he said some code was "stupid". My guess is the campaign against him is rooted in personal animosity.