Basically the difference here is that MNF was written with every character in it having lewd scenes already. In the Patreon version, they have no relation to the main character. They have living arrangement based relationships only, no one is anyone's guardian. In this case, a modder just has to change the text of what's already there slightly, so that everywhere it references "landlady" or "roommate" or something, it replaces it with a familial relation, and bam, you've got incest. Pretty easy to code. Very little effort.
For WVM, on the other hand, the story is written with these characters having that type of relationship with the main character from the beginning. Azel is his legal guardian - meaning based on the laws of some countries/states/etc, anything she did with the MC would be a breach of trust, and gets rolled into the incest laws. Then there's his actual mother, and actual sister, which no one is going to argue would be incest. Here, to include incest in the game, it needs to be changed on a much more fundamental level. One that can't easily be hidden in a "Patreon version" of the game, and patched in later. It would take a lot of work, and if Patreon thought it was something BD was doing themselves, they'd lose their Patreon account and all the money they're making.
I like Willow, Azel, and Wendy myself. I don't hate incest in games, and if they became available love interests, I think that would be awesome. However, I don't think it will happen, and I'm okay with that. This is still an awesome game without it. I agree that it's too much work for someone who isn't BD to do it, for 0 gain. I also agree that it's silly for BD to do it, since they'd be risking their livelihood for maybe a few extra subscribers, when they've already got a successful game going.
I understand where you're coming from. There are great characters that can't be your love interests in the game, and maybe the whole incest angle adds an extra spice for you even, and you'd like to see that. However, if you look at this from the perspective of the person actually developing the game, and making money at it, the risks that would be involved in adding it, and the fact that a 3rd party person doing it would have to do a ton of work to make it happen without getting anything in return, it very much makes sense why it hasn't happened, and is super unlikely to ever happen.
