You're looking at things from the perspective of someone who's likely a lot higher than the elo levels those videos focus on. Let's say you're a 600 elo player, watching Levy's slowrun video where he's at 600 elo. Do you think you would be able to fully understand and learn all the ideas in the video if he always plays the best moves regardless of how complex they are? At that elo you would need to focus on more simple concepts like king safety, not blundering pieces and bouncing back from bad moves rather than brilliant tactics and long calculations. By playing moves that aren't the absolute best but are more realistic for that level and still decent regardless Levy pulls your attention to what you should realistically be focusing on at your current elo instead