It is not do do with the size of the USB but the design of the system.I dont think thats correct. If it was a small USB would handle it easily
Perhaps it has changed since I last looked at it but from a dashcam perspective, all you have is the saved footage (from when you press the dashcam icon to tell it to save) and that footage is 10 minutes long.
Now, if you pull out the USB device and read it in a computer you will see the footage that wasn't "saved". i.e. it continually records and writes to the USB device and when you tell it to "save" it copies that footage to another folder on the device. I wasn't able to work out how log it kept the rolling footage but I do remember once trying to find some footage from the same day I didn't "save" and it wasn't there.