This is like blaming a bartender for someone's alcoholism. At the end of the day, it is the game developer's decision if they want to deliver a finished product and move to another project or if they want to prolong their work like an edging professional domme, making their clients pay, but never making them cum.If you want to blame someone, blame patreon becuase it's patreon who enables and causes this "milking".
Also, limitations in creativity and erotic imagination on the part of devs are to blame. Come to think of it, majority of lewd games here are all alike, exploring the same well-tried tropes and fantasies, most of them not based on real-life experiences whatsoever, quickly running out of steam and ideas. So the devs start to explicitly ask their supporters what new stuff they would like to see implemented and in result, the project becomes a fanfic or commissioned work with too many