Straight from a pinned comment on the discord:
Why don't you guys like mods?
In the days of CoC1, modding was plentiful and unmoderated. This wasn't innately harmful, but problems started occurring when the modded versions were the ones uploaded to filesharing sites and the community misunderstood them to be the real versions. This led to situations like very poor work being attributed to the regular writing team, community members demanding features that the developer had never actually implemented into the real version, etc.
In light of having experienced the situation and deciding it sucked, we opted not to support modding for CoC2.