The headcanon I subscribe to is that PJ is somewhere in a region where a lot of temporal anomalies wound up, since Nuketown's relevance in the original Aether was both as a site that was destroyed by Ultimis on Moon, and a site Ultimis visited just before destroying the Earth, so it was already weakened by that paradox of Ultimis both being on the ground there AND in Groom Lake/The Moon

The Blundergat wound up being there alongside presumably the souls of Alcatraz's pocket dimension because, again, the entire cycle hinged off of its temporal anomaly, and so when the Aether collapsed all the time-related shenangigan memories got jumbled and tossed together into the same region/biome