NIMBYs make new developments difficult to produce, too, actually, and for similar reasons: zoning and environmental laws. New developments also cost more, because you're putting in all-new infrastructure, whereas many old communities are approaching their replacement dates for water and sewer and whatnot anyway. You might as well get the most bang for your buck by introducing more avenues for generating property taxes (ADUs, subdivided lots, and especially commercial establishments).

Also, you don't need to tear anything down. Small neighborhood-use commercial establishments can be converted from existing housing.