This pic shows that MC isn't wearing his chestplate in the trailer. That means that he does not have power for the rest of his armor. That means that he has no shields to protect his armor from the sand. It would allow the sand to damage the exposed metal. The soft black underlayer of the armor would also be exposed and could be damaged even more easily than the metal. His visor was also cracked which justifies the hood over his head. It protects it from further damage. MC's armor is not invincible. Don't think it can't be damaged by sand. Sand get be very bad for equipment even 500 years in the future. It wears down joints and metal of all kinds.