One can only speculate and maybe someone knows the real story but even if they stressed relieved it after rough cuts I bet it continued to potato chip as they milled it.
Even if they managed to achieve good dimensionals after cutting I am sure it takes on a whole new geometry when it heats up in use. Way to much swiss cheese there for a billet cut. I am no machinist but wheels are more symmetric and of course have virtually no tolerance requirements so you can get there.