These are movies nobody is lining up to syndicate, for a company desperate for cash. Why not dump them on YouTube and get a bit of ad revenue? It’s low effort relative to the income it generates. Even if it’s unlikely to make much money.
This is short-term optimization, par for the course with the new Disovery-owned Warner Bros.
https://www.youtube.com/playlist?list=PL7Eup7JXScZyvRftA2Q5h...
Though I would imagine if you were Tom Hanks or Ryan Reynolds you may be upset some of your least popular work is now the most accessible.
https://shop.warnerbros.co.uk/products/warner-bros-100th-ann...
Night of the Living Dead has been freely available for some time for example and is still considered a classic of horror. I'm not sure it hurt Criterion when they released a version of it. People are paying for the restoration and extras.