Effective communication is about far more than whether the reader/viewer can eventually understand the material. Even basic presentation skills can make a huge difference both to the speed at which someone can receive and understand new information and to how well they will retain that information later.

Unfortunately, many academics receive little if any training in good presentation before being expected to lecture or write at undergraduate or graduate level, and while some are naturally gifted presenters anyway, most inevitably are not. Consequently, many career academics have no idea how poor their presentation skills are, how ineffective their presentation is as a direct result, or how much better they could be. They just get stuck at a very low level, but without the kind of introductory/remedial training that would be given to someone whose career involved presentation skills in the professional world. And of course if anyone with broader experience dares to suggest that there might be room for improvement, the instinctive reaction is denial.

A little irony is that some of the most engaging and informative presenters I have ever seen or read come from that same community, but despite the emphasis on peer review in their research work, when it comes to soft skills the weaker presenters typically have no idea how bad they are and therefore make no attempt to learn from their stronger colleagues and improve.