Because the mods are not officially supported by the Vaheim developers, the mods are usually going to "break" (stop working) every time there is an update to the game, and requires that the mod authors update their mods to match the current version of the game... new version of the game usually requires new (updated) version of most mods.

Mods can be used because the developers allowed it, but the devs are not responsible for updating or maintaining any player-made content.

This means that if a player chooses to use mods, it comes with a strong possibility of periods of time where mods won't work, after a game update, or worse, the possibility of your favorite mod becoming un-usable permanently if the mod author fails to update for some reason or abandons maintaining the mod.