Why is Warner Bros. Discovery putting old movies on YouTube?

I assume they get "monetization" from Youtube and they don't need to worry about hosting or discovery. Probably better than doing nothing with these films.

I'm a little surprised there isn't more of this. Building a streaming service is pretty expensive.. a lot of the platforms lost money doing so and really only made it back when they merged into an umbrella of other services.

I'm also a little surprised no one has yet (AFAIK) done the "viral indie release to Youtube" path. I feel like it's sitting there waiting to be exploited.

Movie rights will be a big factor also. Events like TIFF, Cannes etc, while being a platform to show films is also where deals are done, distribution rights are signed always for different territories etc. YouTube is essentially international which may invalidate some pre-existing licence and distribution agreements.

Youtube has the ability to limit videos to certain markets. One example is that the entirety of Mythbusters was uploaded in the past couple years, but isn't available to view in the US.