I don't really care for CGs for what it's worth. I don't doubt there are talented artists out there and it certainly suits some games, but the creator is set on sprite work and I think that's great. There are two main reasons for the reliance on CGs in my opinion - to get around the technical limitations of the simple sprites of RPG maker games, and as an homage to hentai manga and doujinshi where the main sex scenes and page splashes are rendered in excruciating detail next to the far plainer and more abstract story beats and scene setting.
Speaking of abstraction, that's what a lot of sprites are, representations of a character rather than a full CG depiction. With bigger, less abstract sprites, the "need" for CGs should become less, not more. Some of the newer Maker engines have lush and complex environments to utilise and with bigger sprites it means there's more scope for animations too. AI plagiarisation engines may allow for many more illustrations to be included cheaply but in my opinion you should be asking why you would want to include them in the first place.
The other advantages of sprites is that unlike hentaichick.jpg they can be interacted with in the game world, and like actors in a screenplay they can be used for framing and blocking in particular scenes. For instance, you could have your artist draw an image of three faceless guards leering over a blushing heroine, or you could achieve the same thing with sprites and also keep the player character helpless in the background, watching (or just being aware of) events unfold while being actively stopped from intervening in the game space.
In a game with different perspectives you should also ask why you would want CGs beyond portraits, the whole point of the obscured view is to leave the goings on to the imagination. You draw a single CG of a character and the audience sees them get fucked once, use some build-up, a locked door and an audio file and the audience imagines them getting fucked a hundred different ways. Show the knife not the murder, I feel it's more interesting that way.