>>24107975
The nether works differently than overworld when it comes to distance.
In a way, distance can be traveled through the nether, and using portals will allow them to end up in a location equivalent to where they are, linking in a way, a straight tunnel corridor, between nether portals.
Likely, they are looking for biomes they haven't been to yet, to find blocks, ect they don't have yet, to make things out of.
Thing is though, if portals are built too close together, the portals will link to the same one in the over world.
So, they travel far enough, that the portals will create a new one in the overworld, like a door to a long hallway, with another door.