Target audiences are different. More competent people prefer absorbing more dense presentation that leaves out obvious steps and communicates more sophisticated ideas faster, while newcomers need all steps spelled out for a simple enough version of the ideas. Video lectures are usually targeted as people new to the field, or generally less technically sophisticated, such as average university students. By looking for video lectures, you apply a heavy selection bias for this kind of target audience, and so you should expect the presentation to be more transparent. Written material, on the other hand, may target different groups of people. By searching for a random paper or book on the subject, you are more likely to encounter more difficult material. On the other hand, if the topic is popular enough, you should be able to find easy introductory written material as well, you'd just need to filter the material by less obvious cues than it being a video lecture course. One heuristic is to look for lecture notes.