because videos with a "talking-head" are more engaging that slides alone. as was reported in this study: https://dl.acm.org/doi/abs/10.1145/2556325.2566239 ht

because videos with a "talking-head" are more engaging that slides alone. as was reported in this study: https://dl.acm.org/doi/abs/10.1145/2556325.2566239 https://dl.acm.org/doi/abs/10.1145/2556325.2566239 "Our main findings are that shorter videos are much more engaging, that informal talking-head videos are more engaging, that Khan-style tablet drawings are more engaging, that even high-quality pre-recorded classroom lectures might not make for engaging online videos, and that students engage differently with lecture and tutorial videos."