The description points at "affordable housing" (Which means "not market rate", when one of the premises is that the housing is too expensive) and "equitable living". Also one of the texts in the game calls the NIMBYs racist, which is often used as a strawman to smear the opposition to developments like the projects. Finally upzoning would increase property values, but the game constantly repeats "No! I don't want my property value to go down.". (The last point alone is enough to contradict your assumption that the game is about upzoning)
I'm not sure why you even pretend that it's about upzoning and not social housing.
"The majority of NIMBYism I've seen is resisting new market rate housing. So, presumably people do care about duplexes."
What exactly is your job that you encounter NIMBYs so often to get that impression?