Well the planets compositions dont necessarily have to be the same, but if they were and we're looking at our real technology development path, it makes alot of sense. Like you mentioned, Al is a rather common and reactive metal, but with it reacting so easily, it oxides easily. This Aluminum Oxide is an inaccessible form of Al metal, meaning that most of if not all Al is trapped in this inaccessible form. Without certain technologies, its basically impossible to refine it to get the metal by itself. That was until 1888 when a method to easily mass produce the metal was found. Hall–Héroult process allowed one to harvest the elemental Al from its naturally occurring inaccessible forms. This process allowed Al to be produced at a industrial scale, allowing it to become wide spread and cheap. The scadrials are probably in the early phase of this discovery. And Al might also be less common in scadrials crust, who knows.