Nexon's decline in traffic

That indeed seems to be the case. So despite the fact that this link property exists, it would seem that it isn't always being used to its full advantage.

While true, they don't particularly care because it has no bearing on the server itself.
Nexon doesn't really care how much additional processing and resources the client has to deal with because the individual players have to subsidize it, not them. As long as it's within whatever they consider a reasonable burden they'll just keep bloating it.

They care about overhead to their hardware, which having extra maps and mob life does impact. Anyone who doubts this can look at how they designed the client to do all the thinking so the servers wouldn't have to and realize it's true. That's why the game is so easily manipulated. They cut corners to reduce their own costs.