maybe because aluminium often corrodes when in contact with carbon.
How reliable is this statement ? How can chemically inert carbon corrode aluminum ? Or is it chemical resins/solvent found in carbon masts that may corrode aluminum ? Sorry, I don't get it at all (sea salt is a well-known corrosive agent, however, even on aluminum).
(mine RL 530 is absolutely fine as well as a couple of 10 years old North Excellerator 60% carbon masts with alumimun collar at the ferrule junction).