It’s still very active seemingly, after making this comment I started a new play through lol.

Basically each sub region starts off as “disconnected from the network”, so your first expedition to a new area you’ll have no help from other players, only what you bring with you. Once you connect the region to the network, that’s when other players items can start appearing in your world and vice versa. Now it’s instanced so you won’t see everything every single player has placed, just a subset. Now there’s also a concept of “bandwidth”. When you first connect an area to the network, the bandwidth is low so only smaller, lower level things will show up in your game. You’ll start to see some conveniently placed ladders and ropes mostly. So you go from being 100% on your own, to having a little help here and there. Which each new completed delivery though, you increase the bandwidth available, and you’ll see more / bigger objects enter your game world. Bridges can that span a river, timefall unbrellas that let you wait out a storm with some music, watchtowers that can give you a Birds Eye view, things of that nature. When you get the bandwidth really high, you’ll start to see bigger structures like sections of floating highways allowing truck travel, and even underground bunkers that function just like private rooms do in the big locations. So the more time you spend in one area completing bigger deliveries that need to be delivered faster, the game very gradually adds more player support to the game. So the game retains its challenge when you’re first entering an unexplored area, but makes it less tedious to deliver follow up deliveries as time goes on. It’s really brilliant in my opinion. Because while it’s fun to man vs wild your way to new places, it wouldn’t be as fun to keep treading the same route the same way over and over. The way they’ve implemented this system keeps things relatively fresh.

Another factor is that the timefall rain will degrade both your and other players structures over time. So without maintenance, things placed down will eventually be destroyed. You can haul resources to both your own structures as well as other players to keep them repaired. Bigger structures require more resources and collaboration to maintain. You can also favorite certain players and then their stuff specifically might show up in your game more so than random players, so you can almost have an asynchronous “friendship” with someone you never see.