Why not?

Well, if you're self hosting for yourself, friends, and family.. it isn't likely to be a thing you'll want to care about fixing when it eventually breaks in mysterious ways.

Better to use sqlite or just a blob of yaml in a file if self hosting might be involved.

Sure, you’re hosting a few hundred or thousand videos, a blob of yaml can be good enough. I have no history if this project, but I suspect they started out like that. Something like Elasticsearch usually comes into play when you are ingesting a lot of data point very quickly, so I would assume the authors wanted to archive fairly huge amounts of videos.

Maybe I misunderstood this but why does a personal youtube listing / downloading app need ES ? Seems so heavyweight for such a lightweight use.

ES is just a Java-based server, isn’t it? Looks like it clocks in at 500MB which is on par with an Electron desktop app.

It can do full text search (subtitles, comments) right in the ui. It seems to be designed for large scale backups. I use it for a couple hundred important to me or likely to be removed videos and it works excellent, too.

Would have preferred a more unsurprising db like psql or SQLite for my usage, but they also support data dumps so if needed I can escape.