Most MicroSD cards are formatted using FAT32, which has a 4GB file size limit. Newer MicroSD cards, with larger storage sizes, usually use exFAT, which can have a file size of thousands of TB's. To maintain compatibility it makes sense that DJI uses the 4GB limit.
Even though you can reformat SD cards or USB sticks from FAT32 to exFAT so they will hold files over 4GB, it will not change how the Mavic writes the files, and is NOT recommended as it can greatly change the performance of the card.