The fetishes they stick to could be so much more bearable if they didn't spam the same exact character archetypes constantly and if they actually fleshed characters out. But they don't, so everything just melds together and feels samey as fuck.
If anything, staying within your comfort zone too much will just make you a worse writer. Just look at Tobs. He spent so much time smelling his own farts in his little kitsune fort that it rotted his already fragile brain.
But, as I mentioned, this game recruits exclusively from its own audience. The only people who want to write for these games are people who are already fans of these games - thus, the things they are into are probably going to be very similiar to what we already have.
I guess that's why CoC2 sort of... became what it is. You have a group of writers with... honestly pretty basic and limited fetishes that didn't really change or evolve over time, and staying too much within their own comfort zone because it's what the audience wanted. In fact, I'd argue it just gave them more confidence to continue going this route because almost nobody loud in the audience was demanding anything else. They would eat another generic futa/dickgirl that dominates them and acts like a mommy and feel like the more of those characters the better.
Honestly, I kinda understand the temptation. I mean, if the audience really really liked your kitsune dommy mommy wife and wants more of her, why not make an entire village of people of her race? Start focusing on the lore and your amazing original characters, since people liked her so much. It's hard to measure how many people stay for the porn and how many for the story and everything else, right? So might as well put your entire village from one of your childhood fantasies into this popular project that is getting a lot of attention!
This might a very weird that that will result in people here telling me to touch grass, but honestly, looking at CoC2 under the lens of being a massive pervert who can probably explain most tags on nhentai, I kinda think... it's a very normal game, fetish wise? It's not the most normal, obviously - that goes to all Vanilla/NTR/Drama/Wish-fulfillment stories that rarely touch obscure fetishes. But CoC2 is basically a bog-standard fantasy setting where there is a bunch of strong women with massive cocks and horsecocks and you can plap plap plap to get them pregnant preganate gregnant. To me - it's basically what happens when some nerd gets very horny during their DnD session and makes a game based on that. Sure, they are other, more obscure fetishes from time to them, but they are an exception.