why does the graphics resemble other VN.
The decoration on the wall and cakes in the living room is the same as in "The Gift Reloaded"
They both are using the same 3d models and software. DAZ3D makes most most of the 3D characters and pros in both games. The designers are going to just use a quick pre-made 3D model content and not make their own stuff to use in making renders. Designers are going to use what they have or what they can get cheap instead of spending a lot of money.
A serious 3D hobbyist will spend 100-300 a month on 3D models and related stuff if you want an idea of how expensive it can be.
Most game maker are using DAZ Studio, which is free, to do renders, but other software option do exist, like Poser for example, to do renders of the models.
One thing of note is the maker of Superpower on his Patreon site claims he learned 3D modeling, but he just uses common 3D assets and never made any custom 3D content for his game. So an uniformed supporter may think he is making making the models, etc. in his game.
Finally, most of thes game makers never learn basic lighting,rendering techniques, and other important stuff which is why stuff doesn't look great. You can, if you know what you are doing render a DAZ model and make it look like it is a real photo of a person and not a CG model.
Proper lighting, etc. can add considerable to render time so a scene that can render in 3 minutes with generic default lighting, etc. could take 6 hours or even longer if yiu had better lights, render settings, etc. in place and then you still might need to re-render it cause of a glitch in the set up of something, like a light was too bright, etc. So most game makers will just go for a quick way out instead of taking the time or getting multiple computers to help in doing renders for games.
Monica (Larson) for example would look very realistic if the lighting was done better for example. The skin texture used for that character doesn't look good unless you have a good light set up as it darker. An older generation version of that base figure had an alternate less tan (darker) skin that would look better given how bad the lighting is in the scenes.