Magnus played 5 world chess championships. 2 games he played against the previous generation of players who were already well on their way out, and did phenomenally well. 1 game he played against Nepo in a completely even match until Nepo lost one game and went on his somewhat infamous monkey tilt. The other 2 games were against players of his generation. In the 24 games of those matches he ended up with a score of +1 =22 -1. And he was never the one pressing in the classical matches.
Carlsen's paradoxical because he's undoubtedly the strongest player in contemporary times, if not in the entire history of chess, but his world championship matches have never been particularly impressive. And he thinks that his ability peaked sometime shortly before his match with Nepo. So he probably thinks there's a fairly good chance of him losing if he played another world championship match.
On top of these observations, the one player he was willing to play a world championship match against was Alireza Firouzja. Alireza has an extremely poor record against Magnus, especially in slower time controls, had no experience in the pressures of a world championship match, and Magnus would have been an absurdly huge favorite against him.
In other words, he's not playing a world championship matches because there's a reasonably good chance he spends months of work and effort preparing for it, only to ultimately lose and put that mark on his legacy. Right now it's still perfectly reasonable to call him the GOAT, but if he lost to somebody in a WCC match, that'd now always come with an asterisk.
Carlsen's paradoxical because he's undoubtedly the strongest player in contemporary times, if not in the entire history of chess, but his world championship matches have never been particularly impressive. And he thinks that his ability peaked sometime shortly before his match with Nepo. So he probably thinks there's a fairly good chance of him losing if he played another world championship match.
On top of these observations, the one player he was willing to play a world championship match against was Alireza Firouzja. Alireza has an extremely poor record against Magnus, especially in slower time controls, had no experience in the pressures of a world championship match, and Magnus would have been an absurdly huge favorite against him.
In other words, he's not playing a world championship matches because there's a reasonably good chance he spends months of work and effort preparing for it, only to ultimately lose and put that mark on his legacy. Right now it's still perfectly reasonable to call him the GOAT, but if he lost to somebody in a WCC match, that'd now always come with an asterisk.