Are you sure about that? Robots, yes (well they are definitely at least partially biological but yeah), but do we have any evidence that their shape derives from their original pilots? Do we have any evidence that they were ever piloted by anyone who wasn't a Tenno (and all Tenno are children so Frames certainly weren't modeled after them)? Silver Grove Spoiler

I was under the impression that the current prevailing theory was that frames are infested flesh given form and contained within armor that is controlled by Tenno (as evidenced by the original Rhino's behavior and, possibly, the infestation that has broken out in our orbiters). Maybe the theories have moved past that but I'm not sure, I remember a lot of people theorizing that the infested outbreak came from the scene in Second Dream Spoilers.