The reason behind this is twofold.
First of all, one of the great additions to Unturned was the addition of NPCs and Quests and it spiced up the gameplay. Unturned no longer became simply loot and survive- and now there was the adventure component.
Modders have come up with lots of intricate quests and NPCs and adding them to official maps or modded maps will give them something more to do, which again, improves player retention. The only way this has to be done is by editing the official(or Workshop) map, which requires an unlock and reuploading it as a separate mod. Despite the only difference being the addition of NPCs, players who only have the original maps won’t have access to the server unless they have the “edited” map. Its just how it works. They are then forced to go find the map on Workshop and subscribe to it. This may sound simple, but in fact is a huge turnoff to joining said server.
Here is the 2nd reason. The Workshop is absolutely FLOODED with a bunch of ripoff/duplicated maps. Only difference? Custom NPCs.
This might alleviate the issue
I think NPCs can be reclassified as a “Structure”, or have its own class akin to Barricades and Structures, instead of it being an Object
EXAMPLE With Barricades and Structures, you can make a massive building on Singleplayer, copy the Structures.dat and Barricades.dat file, and place it in the “Levels” folder in your server installation. Voila, the huge building you made now shows up on the server.
A similar capability for NPCs/Quests would be much appreciated