At least according to Wikipedia, small amounts of carbon (< 2.14%) in the final alloy are an important component in controlling the ductility, which agrees with what I thought I remembered from materials classes (although I am not a materials scientist). Obviously not using the Bessemer process drastically reduces the amount of carbon necessary, but trace carbon is important.
Silverblue doesnt either… I think you’re right, it’s an immutable distro thing.