"Redistribution is prohibited"

And what exactly can they do besides banning patrons? Even then, they can only do that if they know exactly who did it and in order for that to happen the person who "leaks" it has to have the same username on some other website as they do on Patreon, but that's the magic of the internet; people can have anonymity. Also, what exactly can they do from a legal standpoint? Trying to sue or prosecute anyone from posting these images would be frivilous and probably cost them more money than it's worth.
Besides, thousands of people will see this image in a month or so anyway, so what does it even matter if it gets out there for everybody to see?