While never giving an official release date both Guerilla Games and Sony have both suggested that the Horizon: Forbidden West was aiming for 2021 to release. In an interview with Hermen Hulst earlier this year he also said the same, with the caveat of nothing being set in stone.
Given the state of the world currently, coming out of but not quite over the Covid-19 pandemic, with multiple big-name games being delayed this year I think it was dubious to expect Horizon to hit its aimed release date. According to what Jeff Grubb has heard, this is exactly the case.
Disclaimer – This information has not been verified, therefore this is not factual.
During his podcast for Giant Bomb, which is behind a paywall, Jeff Grubb discussed Horizon: Forbidden West and what he has been hearing about the game. While not outright claiming anything, he pointed to what people have been telling him, mainly that the game was going to be delayed into 2022.
His track record on the Switch Pro aside (Since Doug Bowser has adamantly suggested there is no 4k Switch planned for 2022) Jeff Grubb is usually right about these things. This is also not the hardest rumor to believe. Most companies are already working on messed-up schedules for their games thanks to the pandemic and the Netherlands, where Guerilla Games is based, only recently experienced another lockdown.
Jeff Grubb also stated that he is hearing a new State of Play might be coming in September. He did not make the connection though if this news would be confirmed during the said event or not.
In light of the circumstances, this move seems far better than trying to force the game out. Several studios have found themselves in a very similar situation, and though it might mean waiting I think most games con appreciate that if it means getting a polished experience.
Source – Reddit