TikTok is focusing on longer videos these days via allowing the video length to be longer, because short videos are a money sink. Meta realized this already as well, as Mark mentioned that they're losing 1B a year on short form videos.
Engagement. Ads in short videos are more likely to be skipped or navigated away from compared to an ad in a longer video when the user is engaged and more likely to stay engaged with that content through the ad.
Youtube has excellent documentaries, movies, news and commentary if you go beyond the default Mr Beast sloppa.