I think a factor is overestimating just how many people 'get into' YouTube culture. Only roughly 74% of American Adults use YouTube[0], and the average daily watch time is only 42 minutes[1], not much time to explore and watch videos outside of your own interests. Vsauce's videos are great (including the recent ones), but they're mostly a remnant of YouTube culture past, and 10-20 million views a video[2] is not a lot in the grand scheme of YouTube's 2 billion strong user base[3].
0: https://www.journalism.org/2021/01/12/news-use-across-social...
1: https://www.emarketer.com/content/us-youtube-advertising-202...
2: https://www.youtube.com/c/vsauce1/videos
3: https://blog.youtube/press/#:~:text=Features-,YouTube%20by,t...