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

Old movies have been available on various "free ad-supported streaming television" for a while now, so I'm actually more surprised it took copyright holders that long to realize that Youtube also shows ads and doesn't require people to install some wonky app that might or might not be available for their platform.

Of course, region-specific copyright deals are incredibly complex etc. etc., so I could imagine it was just a matter of waiting out until the last person putting up a veto retired or moved on to other things.

I assume that bandwidth is by far the biggest cost for running your own streaming service, so letting Google take that hit makes a lot of sense.