Thanks a lot for the informative replies.
My experience went like this. I didn't feel attracted enough to what I saw from commercial visual novels, to be willing to pay for it, mainly because of the lack of visual variety/realism. What I did buy is Life is Strange and a Batman tell tale game, which has choices and where you can freely walk around the scene, but I consider such games out of my reach (skill/time/money) to make on my own. I finally downloaded a free novel out of curiosity, which was Everlasting Summer. I loved the introductory part until you arrived at the school because of the beautiful screens. I did start to skip through text rather quickly though because I don't like extremely descriptive stuff. But when you arrive at the school, there's a character suddenly popping up on a pretty but also quite empty background and it continues like that throughout the whole story with the exception of a few unique images which are nice but are too rare for me to enjoy the story.
At that moment I did feel like I wanted to be able to make my own visual novel, but in a more realistic way, where you see everything on screen like you would in real life. Since I can't draw well, I went to search for how to make my own characters. The first VN engine I used was Novelty and on the forum I could see someone making pre-rendered novels with it, but it all looked very basic. Environments were very simple and characters looked quite dull. I first tried things with a free character generator and free to use backgrounds and then I finally moved on to DAZ and started buying stuff in their store. I didn't even know the word pre-rendered at that time. It's only much later that I realized that pretty much every pre-rendered novel is 18+.
When I started using DAZ, they had just released their genesis 8 model, and I thought it looked really good. For some of the important characters in my story, I spend between 1 and 2 hours making their faces unique and I really like the results. Render times can be annoying, but I can still do other things at the same time, so it doesn't bother me too much. I don't know why someone would spend a week on one model unless it's done with something like blender(?). Making good expressions can be a challenge, but in general I am quite satisfied.
The thing is that I don't like the usual concept of VNs. Characters typically just pop up on screen and disappear again which is also how actors are programmed to work in engines. There's no realistic integration into the background (which also means no realistic shadows). They might have some unique expressions/poses for certain scenes, but typically you will continue seeing alot of the same images throughout the story. Sometimes things happening are simply described without much or any visuals at all. There's no realistic detail in hair/clothing/skin/eyes. There's often just one camera angle for each background. To me this is all a lack of immersion, which makes me lose interest in reading through a lot of text. It may be that drawn images are more natural/expressive, but if they are never a real part of the environment, if you see often the same images, if their hair is not very detailed etc, then that is not natural either, so I think you can win on one side and lose on another.
From what I could find, Illusion Soft/Tea Time is also just making porn. I wish there was at least one example of a studio trying to make novels with 3D prerendered images, characters realistically integrated into backgrounds, telling compelling stories that are not an excuse for having sex scenes. Something like tell tale games, but without camera control/walking around. It may be that now the typical public for VNs is oriented towards a certain style, but maybe there's still a hidden potential somewhere that hasn't been tried enough yet.