That's not my understanding of it's history; it was originally planned to have, potentially, multiple porcelains, but that idea died of a couple years back.
I believe that is the root problem of git. Originally, the assumption was: porcelains will provide a nice UI, so core git can leak implementation details. However, it turns out the implementation details are so simple and intuitive for many developers that core git is now the dominant UI.
For example, the multiple use cases of 'checkout' or 'reset' are quite intuitive, if you have the implementation in mind.
