I think the biggest factor is that 99% of the human spieces is too easly pleased(see: Why visual novels exist)
But i think out of the choses given:
Characters (Personalities and their designs)
Is the most common reason.
I remember lilliy, stephanie, jassica, nora by name from the lab rats 2 game.
I remember jessie from moter home.
I dont remember blackheart games characters names.
Despite being very populair it is an accepted fact you play those games for the sex scenes.
Not the story.
I remember allie, stephanie, maggie, sandra, lauran's, from superpowered night city.
Chealsie(or something like that) awakend my love for fishnet clothing.
A story is only as good as its characters.
And 90% of the characters are too eager to sleep with you.
I dont feel like a corrupter in most corruption games.
I dont feel like a rapist in rape games.
I dont feel like a lover because romance games are boring.
Urge to molest(both) wherent good games.
I mean they where games which puts them about any visual novel by default.
But there characters where interesting, the main character was interesting and the risk management was enjoyable.
Likewise in lab rats 2 events change depending of the character stats.
How far you can go, how obedient they are too you, how normalize sex is, etc.
Sometimes i cheat just to see how the events change(for example i cannot get my aunt corrupt enough for a full sex scene early game without cheats and that scene is only early game)
Likewise in superpowered night city i get difference scene depending on stats.
Ow sure turning them into sex starved sluts is an option.
But what if i want them to be normal but mind controled.
That is an option.
What if i want to make them be fully dressed sluts.
That is an option.
What if i want them to be sexy clothed prudes.
That is an option.
The best games in my opinion give you the tools to create the perfect harem.
Turning a prude into a slut is done so often it is boring.
Turning a slut into a prude would be fun once as a new experiance.
But the real joy is to turn woman into your prefered fetish.
Lets take hentai highschool+.
Its biggest flaw is that you can only turn them into sluts.
It has the setting and tools to allow you to create a cult of personality but the gameplay doesnt allow it.
A big part of what makes free cities so great is the way you can reshape culture.
You want to create a culture where slaves are seen as valueable possesion and need to be threated properly?
You can.
You want slave being hurt be the highest virtue of your city?
You can.
You want to create a cult of inbreeding?
Again you can.
What seperate games from movies, books, and visual novels is that it is a game.
And you get to influence it by your actions.
My advise to dev is to adopt the mentality of:
This is the problem.
Here are your tools.
Go fix it.
Aka create a game that allow players to use the tools of the game to fix there problem there way.
Rather then the dev way.