Well, most of the "standard" VNs written in Renpy do not require a dedicated coder, since the coding part is simple enough to be dealt with by the artist himself. Adding another person to such a project would simply overcomplicate things, adding need to coordinate and negotiate control, and reducing the chance to apply unplanned changes on the fly, for not much of a benefit either in development time or quality (a.k.a. "nine women will not give birth to a child in a month"). I'm willing to bet hiring a developer in such a case would only save some weeks time to a release - not much in the grand scheme of things, and not enough to justify having another people on a semi-permanent payroll.
Also, the author's Patreon existed well before the game. His first posts are dated 2015. As such, back then people were already financing CyanCapsule for his art (pictures and comics) - in fact many of the characters in game take inspiration from his previous efforts (Emelie herself existed before the game).
With this perspective and context, CyanCapsule is not being paid for the game alone. He's still being paid for being CyanCapsule, and producing his niche art, in the form of a game or whatever else. That's the Patreon approach, and the usual is true: there is no contract, and very few obligations. One can not agree with it, and he's well in his rights not to finance an artist which he finds too slow - but that's all there is to it. The alternative is simply not having his amazing art - certainly not under the same conditions.
