My original draft for this post was:
"How come cross-media franchises rarely utilize the video game format?"

But I just discovered something more important. Now, this information is a bit paradigm shifty, so if you don't want your mind blown, and your world changed forever, close this thread right now.

Okay. So, there's hentai manga, and there's hentai anime. But between manga and anime, there's "voiced comics" [ボイスコミック]. Voiced comics are hentai manga but in video format, and get this, with VOICE.
https://www.dlsite.com/maniax/works/type/=/work_type/VCM

No more, you will just fap to a 2D girl by looking at her 2D body getting railed. You will now fap to a 2D girl by looking at her 2D body AND listening to her 2D moans as she is getting railed. Check out the trailer in the link.
https://www.dlsite.com/maniax/work/=/product_id/RJ340486.html

It's a game changer.

Still not convinced? Here, /v/, try this trailer. I know this is your type.
https://www.dlsite.com/maniax/work/=/product_id/RJ01257115.html

/voice/ doesn't want you to learn about this. They are a cult, they're in /h/, but fap to females talking instead of 2D drawings of females. You can pirate from anime-sharing and mikocon. You can go visit /voice/ in /h/, but I'm warning you, they're not to be trusted.