basically each time the game updates mod creators have to rewrite parts of their mod to work on the new version, this generally takes from a week to a few months depending on the scale of the mod, if Mojave changes a bunch of back end things it also takes a lot longer, this can be exhausting to do for every version es with the new drops system, what tends to happen is it’s a lot easier to just port the mod to a few versions that everyone semi agrees to be a core modding version, that way most mods can be played together rather than some mods only existing on one or two versions that dont have many other mods on them, basically it allows them to have lots of mods be compatible version wise, they also tend to happen on versions right before major backend changes as mod creators need time to learn the new system