Pirates steal every kind of commodity they can, then they bring it to a Junker depot or the closest friendly base. Junkers will not offer the maximum price of that commodity because they do not need it, they accept it sure, they will make use for it, but they don't need alluminium as bad as a station with a production line that eats huge quantity of it every hour. It's a matter of supply and demand.
If you bring it in a ship that was designed for shipping that kind of product, the time it takes for the product to reach the production line is shorter. Imagine in real life if bricks were delivered to a construction site in an oil tanker. Sure you can load it with bricks, they will fit there, but loading and unloading is absurdly difficult, bricks will get damaged and i don't know who would accept that delivery.
Your second and third paragraph explain exactly what i mean about the proper ship. The lore even talks about that: ALG Heavy Mover
Quote:Incorporating extensive rad shielding and magnetic storage units not seen outside of heavy capital class engine reactors, these highly specialized vessels are hardened to withstand the toxic nature of the cargo they move.
