I've only looked at the code via the HTML document in the download, from what I understand they basically used a framework to make the game but it's meant for those short "couple internet gifs here and there" stories rather than a massive rape-town simulator.
Between that and some red flags in the code (dodgy methods, inconsistent names/style), I'd imagine development itself is hard solely because they have to wrestle the code. I tried opening it once of the recommended framework/program (Sugarcube in Twine) and it basically shat the bed, so I imagine on the dev side that is an issue as well.
I reckon after they got that guy's pregnancy update, the best plan of action would be to refactor the code. The gameplay itself is pretty modular so if they made a solid foundation they would have an easier time updating new stuff (ofc this is from a perspective of the .html document, I'd imagine it's cleaner on proper software).
Afaik, the game started with Twine. (Essentially the game content is hidden in the HTML file and there is some JS-magic which transforms the hidden parts into visible parts turn by turn.)
But this got out of hand
very soon.
At some point they switched to Tweego. It keeps the SugarCube engine with it's JS-magic. But the game content is spread over many twee-files like source code in a conventional programming language. Tweego is kind of a compiler which turns these twee-files into this huge HTML-file you see. No problem with soiled bed sheets here^^
But since it's HTML and JS at the end, there is no actual limit.
A lot of game mechanic has been moved to JS.
Idk if they call it "refactoring", but they do it all the time. The changes "under the hood" between 0.3.x and the upcoming 0.4 are huge.
Despite all the preggo stuff, the overall code quality has improved a lot. But the afterpain of all these changes will take some time to fix. (18 year? *cough* *cough*)