The STW universe and Reality Zero were once a combined reality early in the Zero Point's lifespan. However, soemthing happened that split them into two.
The STW universe still had fragments from the zero point and despite both developing independently— many aspects and events between them were shared up until the Zero Point was destroyed in Season X and that link was severed. It has since slowly retethered— but is nowhere near as strong as it once was and remains unknown if it'll ever be again. The only thing that is certain is that for the longest time, Reality Zero would have been destroyed eons ago as many attacks from the Last Reality that were intended for it were redirected to the STW universe due to their Zero Point Frequency being near identical.
Fortnite Headcanon #1294
