In theory, it isn't that difficult, in practice writing _accessible_ text takes a lot of practice and feedback. Letting go of your own biases towards base levels (curse of knowledge) is something that already trips most people and what people find really difficult to overcome.

Which is why the statement you are responding to is often more true than you might realize. Because these people have had a lot more practice in that specific area. Although not all of them, that would be a generalization in itself.