Simply put, Pass Block and Run Block were leftovers from CurrentGen. The decision was made to add some new offensive line ratings (years ago) - and the last 2 were not taken out altogether for whatever reason. I believe they are still being used in limited ways in sim code.
I never said they do "nothing". My statement was that I know for a fact that the primary ratings that matter for Offensive Linemen are the 4 we've been talking about - not P Block and R Block.