>>47417999Once you move away from strict game logic, it kinda makes sense. Not every pokemon is going to be the same size, and for ones where you can force an evolution, like say, with a moon stone, there probably would be size variations depending on how grown it already was. A tiny Nidoqueen would likely be the result of using the stone immediately on a freshly evolved Nidorina.
This gives us some pretty funny visuals, when you think about it. Imagine hatching a Scyther and immediately trading it with a metal coat, and out pops a foot tall red metal bug with oversized pinchers that it hasn't grown into yet. Or Arcanine! Imagine a tiny puppy Arcanine.