Sony’s controversial PlayStation Network requirement for its PC games is once again in the spotlight after the company delisted the original Horizon Zero Dawn on Steam and the Epic Games Store and added the PSN requirement to the upcoming single-player remaster.
This is not true in the literal sense.
You cannot redeem HZD keys, and buy it as part of a bundle with both versions. They stopped selling it standalone.
So you can get the upgrade for $10 if you already have it, or wait for a sale on the bundle.
But in either case you can still play the original release without the PSN requirement even if bought after the remaster release.
For now
Well they have structured the Remaster as a DLC upgrade that requires the base game license.
So they would have to delist their new listing and create an entirely new release.
Honestly 99% chance they did it this way to preserve the review history of the original game on the Remaster.