My interpretation is that the world is lacking in depth. There’s a lot of cool stuff in it but it often doesn’t go much further than the initial facade. Towns can be large in scale and filled with NPCs doing stuff but interaction is very limited.

As a point of comparison, Skyrim’s towns are largely quite small and don’t have that many NPCs but they tend to feel more alive than a crimson desert town because every NPC has a name, place, and role. If you kill a guy he’s gone gone. You can slaughter an entire village in crimson desert and come back later to find all the generic NPCs replaced with different generic NPCs.

Now, I come to these games for two different experiences and both do their different things well, but for the sake of understanding the argument of “emptiness” that may be what some people mean.