Google Search, Amazon, Netflix-- my guess is there's just have more structured data for these recommendation systems. Amazon and Netflix get high-quality descriptions and information tables about their videos/products, Google Search has to do a bit more digging, but it has the whole text corpus link structure, etc of a site.
Spotify probably has it a bit tougher, but my guess is playlists play a big role as they are curated clustering of similar music (as opposed to just a "folder" to put all videos in a series, like they are on YouTube). Music itself is also probably much easier to analyze than video: extract the BPM and frequencies and you can tell a lot about the composition of type of song it's from. Video on the other hand-- you can do very computationally intensive CV, but that won't tell you much about the mood, meaning, genre, etc. of video something is.
YouTube many times will have to go off a title, a very vague description and a ton of irrelevant comments.
Edit: Actually, they have captions. I'd assume dialogue could give them a lot of relevant information, who knows ¯\_(ツ)_/¯