Quick answer: most adult games on Patreon aren't built to scale up development based on an increased budget.
The most successful adult games on Patreon all each have their own unique style, that may or may not be easy to farm out to contracted artists under a lead art director (Breeding Season/Cloud Meadow operated like this, which is the only one that really comes to mind). A lot of people say DC's style is simple enough that any competent artist should manage to keep up, but you also have to remember that the hiring pool willing to work on an adult game, not to mention specifically THIS particular adult game, is probably extremely limited. I mean, go to Hentai-Foundry, deviantart, or pixiv and find an artist who both does remotely similar style work AND is willing to commit X amount of hours per week for this huge project.
So really, the structure has to be in place from the beginning before the project even launches. You have to have art guides, a pipeline, management, etc., not to mention you would probably need a contractor lined up or else find yourself in this situation where all of your applicants are not compatible/up to your standards. That's not to say it isn't possible or hasn't been possible for the last ~3 years of development, but the right pieces have yet to fall into place to make this happen.
Long story short, money does not guarantee a solution to the bottleneck art problem. What it does however contribute is that DC can work on this full time instead of another dayjob, he hires others to take care of the coding, animation, website/community management so that he can focus solely on writing and art.
