A ring is not resized by scaling the whole model. Scaling a ring up makes the head and the stone seat grow along with the finger, which is not what a larger ring is. Instead the shank is spliced, so the band grows and the rest of the piece stays the size it was designed to be.
Each size that comes out of that is then measured separately: its own volume, its own minimum wall thickness, its own manufacturability check. That is why the weight quoted for a size 11 is a measurement rather than a size 7 multiplied by some factor.
It is also why the sizes on offer differ from piece to piece. As a band stretches, its wall gets thinner, and at some point it drops below what can be cast reliably. When that happens the size is not offered at all. You are not looking at an arbitrary range; you are looking at the point where the metal runs out.