A game like this is with this level of details, is extremely time consuming to do. Art and posing takes a lot of time, this game is using those two things to a degree that isn't seen anywhere else. They are varying animations/poses/illustrations every step of the way, first of all you have to make all that art which takes time and is physically exhausting and then probably reedit it a lot of times after on to make sure everything works in the context of the game.
The developper has to put that in the game, just doing the prep work, setting up the images, creating layeredimages to support those take time, then comes the posing which is one of the slowest task possible, you have to choose what is gonna be the mouth/eyebrow/bust/eye on each individual character in a sequence, and if you want your posing to be as good as it can be, this requires thorough testing. This game has insanely complex posing, it goes beyond simple mouth/eye/eyebrows, it's changing constantly like an animated movie.
You have to reload the game each time you change something to see the results, the reload time isn't insignificant and the game gets bigger and bigger with each release, it also make it slower.
Don't shit on them, there is a commitment to a certain level of detail in that game that explains the delay, it's apparent to any devs that ever worked on ren'py, if they wanted they could drop the level of detail and sacrifice the way things flow so well in certain scenes and probably have it much sooner but they have chosen an hard path and they are getting shitted on for that, it's kind of fucked up.
