Probably because the rocker arm is not rotated so the oil hole on the shaft is aligned with the passage in the rocker arm when the cam passage is align in the block to provide oil pressure work
I groove all my roller cams # 4 cam journal so they will oil the rocker shafts full time, they will shoot oil out the rocker arms that way thumbs I am using around a .040 oil restictor in that oil passage now, the restrictor size depends on the type of rocker arm, extruded or bushed get a .080 restrictors, true roller rocker get the smaller sizes thumbs

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)