It didn't happen because Milo What'sHisFace is too young to be Adrian Pasdar's twin. Unless it's all whacky time-space continuum and then it's just crazy town.

Yes, I figured it had to be something to that effect with casting. And as I mentioned to someone above I'm a big Nathan fan, so while I invisioned them as some physical meshing of Adrian & Milo, I was probably unconsciously leaning more in the Pasdar direction.