They were allready so small that they looked very pointy. If you want to have more roundness in a smaller area you need more polygons for your wireframes. Thats why charackters today have more polygons in their faces than they had at that time for the whole body. And more polygons making up one breast than they had back then for their faces.

Nevertheless, im sure one can reasonably argue that if big breast were universaly seen as negative (i personaly prefer them smaller. Ideal size 2 hands full imo.) they wouldve worked on a better solution.