I don't know if it makes any sense to assign blame here to another party than Sony. As a customer who bought a license to watch these shows, that's the company that you have an arrangement with. It seems that their licensing arrangements with Warner Brothers were limited time, and either WB isn't inclined to renew them or is asking more than Sony is willing to cough up.

Probably a combination of both if I had to guess. WB is seeking to maximise the value of their own ~HBO~ Max streaming platform, so they want the content to be exclusive and not license it out to others. At the same time Sony is probably not excited to keep spending cash every few years just to keep content available to customers, they're not making any additional money from that.

So the end result is the current situation. Obviously customers agreed to whatever terms Sony put in their EULA at the time so I'm sure it's legally covered and whatever, but it seems pretty scummy and misleading nonetheless. Like, if they were honest on the purchase screen and said "you can pay $20 for the right to watch this season of mythbusters, but any time we like we can take it away from you again and there's nothing you can do," how many people would have bought that? But effectively that is what people bought, they just weren't aware.

Yes, it's Sony's fault.