Origins tend to be rather more spread out, and it requires pretty high density to generate more riders than a Park-and-Ride, which generates one rider per 400 SF. A three-story apartment is actually worse than a Park-and-Ride--not everyone in those apartments will take transit, and parking + landscaping will take up over two thirds of the parcel. A 2-3 acre bus depot will likewise collect more riders than a garden apartment. So making a fuss about the density of origins near a transit station is rarely worthwhile across most of America.
Further, origins highly concentrated on a small fraction of land parcels, and highly concentrated on buildings located within those parcels. As getting places requires getting to the front door, it's that access that matters for transit supportive density, while most origin destination calculations are made using metrics like units per acre. Pure geographic coverage is a terrible metric for access--most of the land is empty or occupied by things like private yards.