What can guarantee that his muse won't change in 6 or 10 months?
Absolutely nothing.
That's why I see patronage as "I'm supporting this dev", not "I'm supporting this game". If patrons aren't willing to give money to the dev to follow his muse, and instead give money to a dev to support a certain game, they should pull their support if his/her vision diverges from what they wanted.
Unfortunately, the threat of this probably puts pressure on some devs, so they keep working on stuff they don't have a passion for, to keep the sweet Patreon trough flowing.