Multiple reasons. Running the gamut from personal to financial.
Bottom line is that most of these content creators spend a lot of time and effort into creating these models, let alone the game experience we see these characters in. Keeping their character sources private allows them to leverage our interest in the attractiveness of these character models and our desire to see more content of them.
If they were to just allow their fan base to download these character assets, you'd subscribe for a month and be gone for the foreseeable future until there was maybe another character you wanted. And that's if there wasn't some asshat that decided it was okay to release that patreon content for pirating, which would happen, always does.
It's part of the reason why there are those of us, willing to support these content creators through Patreon and other sources. Sometimes we want to see more of the story and character development. There are those that are interested to see more gameplay or features set in this fantasy world. But at the end of the day, we play these games because we are invested in that virtual ass.
I can't say I blame them. I've tried recreating some through the various engines. I've gotten close with some but it's just not quite the same.
If you're that interested in some of them, ask in the threads for a save file or see if there's a walkthrough for it. Most of these games have a skip button that fast-forwards through all dialogue. Some games also have a patreon code that can be entered, if they have a gallery option. Pick your poison.
