You do have a strong point, in that homeowners are eager to approve plans that allow for ADUs but disallow anything slightly larger. Homeowners already have housing, don't often need more of it, and like having complete control so they approve plans that allow ADUS with the knowledge that it won't account for any significant new housing, and new housing is directly against homeowners' financial interests.

But in reality, the political choice of "let's build A, or B, or C" doesn't exist to maximize the effect of housing. People overly focus on highly regulating to a specific type of housing to prevent anything from getting built.

Let people decide for their own what type of housing they want, and all of a sudden we'd have enough of it. That's the biggest fear of landlords and homeowners.