They just be mad because they can no longer control what sort of content that gets added in the game. Especially when they have "the Tobs" syndrome, they will became floppy pp with uncultured and unchecked writing. Oh and don't get me started on the possibility of everyone having the favourite "incest patch" or content in game. They would be in huge trouble if that happened. It could turn out Kinu 2: electric boogaloo. And patreon would blame it's their fault and ban their account. And who wants to get the same treatment as kitteh666 from the old CoC mod. So modding is very unlikely to happen.
I mean, I understand some of the points here. I would like for them to still allow it at some point. Maybe when they finish the game... Ahahah, yeah...
But modding does add more life to a project. Sure, a lot of it sucks or is to edgy, but hey, you do not walk through gold mine expecting just gold. And I am not sure how patreon would have any right to shutdown a game because of a mod.
And If they can do that, just switch to other donation sites. We all know that all of us horney people will follow since it is not like we can get these types of games anywhere else (at least with this amount quality content).
But honestly, the biggest reason I can think for why they banned mods are
A: If people would be to make there own content for the game, people may not feel obligated to pay for the making of the game. Since most of the games with mod support are finished, they do not have this problem. They maybe fear that people would just stop paying them since other people would make content for free.
Now, while this may be cause for concern, we could argue that If there content is good enough people would continue to pay for continues production. Since most of what they produce should probably be better then what some schmuck in his mothers basement can produce. At least they are profesional enough to pay for there basements.
B:They do not feel comftroble with how some people would handle the mods.They may not be comftrable with idea that anyone with basic talent for programming (Not me) having a capacity to alter or add to some questionable content to specific characters. Like giving Brienne a cock or some sick shit like that. Or adding some of there OCs that would not mesh well with the game.
And Lastly C: People may not be able to tell which version of the game is vanila one if people start making compilations of various mods. This one seems least likely since all of that could be avoided if they just write that it is a mod on title screen, but some people may not do that.
Still yeah I wish we had mod support.