make them "look right", and scale-up the bits that are too small to reproduce to exact scale. All of which the old mold makers could do, skillfully. We have all seen the results (i.e. Trumpeter) of what happens when you don't do one or more of these things correctly. (I now they were not 3D printed... I'm just using it as an example of computer generated "models").
And the Trumpeter people weren't kids doing the work just for fun, or even serious hobbyists. I'm just not sure there are very many people that have both the technical skills combined with the artistic skills needed to produce really nice 3D printed models. (And has anyone yet figured out how to print a part as large as a model car body that doesn't need extensive sanding, and other tweaks, to make it as nice as an injection molded body?)