It was originally made with NPCs in it, which made it play better as a single player game - but they took them out and focused on multiplayer (amongst other stuff) for… 10-15 years…

As in your case, I think 10-15 years ago, I probably had enough game-playing friends and enough “lack of responsibilities” to play multiplayer things (before it had any multiplayer) but not nowadays.

There have been a few reasonable NPC mods over the years (and probably there still is?) - but we’re still waiting for NPCs to be put back in “properly”.

In theory, version 43 is the NPC one, which I’m looking forward to.