Its the fact that every goddamned update, there's a new character and the main plot isn't even being worked on. The worst part of it is that those new characters only serve as Blue Balls and becomes entirely irrelevant for how many years because he keeps adding again, new characters.
Author should atleast finish a storyline, decide on Who and How many characters are central to the game, then revise it at the end. (I know how agonizing this is, which is why he needs to keep his head straight and not get sidetracked)
All these new characters and unnecessary content is only going to be a headache when he finally gets to close on completing this game (which predictably, won't be released cause its been 2 years and there's still not much to the Main Dish).
Like why do you think there are lot people starting to comment that "each update gets worse"?
Hell, the main point of the game is Farming, but with sex. Something that hasn't been done to this day. Game is going to have more characters than Darth Mickey's empire or hell, Stardew Valley.
this phenomen actually has a name.
Feature creep
when a gamedev wants to add so many things it becomes impossible to finish a game, not to say the ideas and features the dev wants to add are bad, mostly they are great ideas but it just becomes to much to handle.
as you said, the dev "should" have a general guideline to finish first and do all other stuff in dlc/addons later on. or if they have no guideline a limit on how many stories he works on simultaniously (usually 3-4 before it gets complicated)