Right, but Steam still let's people who own delisted games download and play them forever. (Well, assuming they're not live service games with no servers, but that's not a Valve problem.)
I believe you can still activate keys for delisted games. Meaning if you find a shop that sells them, you might be lucky. I never did that, just read reports of this. So can't actually verify if this is true. Provided there is no additional third party launcher or activation that hinders this.
One example are most telltale games which still are still playable but not purchaseable (poker night at the inventory being the most recognizable for me since the associated tf2 items are also now that much harder to obtain)