The short answer is its not built yet.

The long answer is its a new system since it sort of mimic’s the player buildings in form and function (such as destroying foundations brings down walls), but also has the feature of respawning as PVE content.

The idea from what I’ve gathered from the streams is that they want to get the system so they can easily implement more such content (though smaller) and allow modders to add their own fortifications. I assume the one added to Siptah will be a testbed for that upgraded system.

Its not as simple as copying and pasting the fort from Exiled Lands, not yet anyway. I personally can’t wait to see what modders are going to do with this new system. Dungeons with walls that can be bombed like in Legend of Zelda would be really cool.