Stock afcad that came with your airport, all international flights parked in cargo. Why?
Most likely because you are not using an AI product with proper airline codes or no AI product at all, so the sim will park them according to parking size only, because all gates are normally flagged as GA, in order to get rid of default ground traffic vehicles, which is a quite common method used by many developers.
When the AI plane has an airline code, it will take precedence over the parking type in the choice of the parking.