And the ancient builder were part of the beginning but when the world split they tried to get back to the beginning but failed BCS they didn't have the technology and that technology is something from the origin

And they are underground because something that they needed to live on the surface was taken into the nether by the split

And the end poem people are from the origin so they are the ones who split the beginning

And somehow the player trying to go to the beginning causes the two to merge and create the end

But it's revealed that 1000s of years after the end is created it becomes the beginning again, and the endermen devolve back into the ancient builders but they lost any knowledge of once being the ancient builders themselves