An 18+ patch was originally planned, and it's true that often means CGs.
When we came to actually creating the patch content, we opted to write the story first, and then consider how to fit it into the game (as opposed to drawing an image or two and then writing to fit the images).
As you've probably seen, there ended up being quite a lot of that written content (definitely more than we'd originally guessed we'd have). Beryl and Chris are in an interesting situation, and the ideas flowed well.
But that then led to the realization that to adequately illustrate all the action would take a tremendous amount of effort (and we're all too aware of how often you can hit an h-scene in a game, and so much of the story ends up mismatched to the static image, and we didn't want that either).
So we were faced with a choice - we could add months (a lot of months) to our development time (for content that not all players will want). Or we could cut one or more of the explicit scenes out entirely (but we liked them all!)
And neither of those were very appealing choices! So we chose to focus some additional art resource within the main game, and allow our readers to use their imaginations to fully picture the 18+ scenes in their entirety.
Beryl tells us that she appreciated the extra time she got to spend with Chris, too. ;)