SanDisk SecureAccess is a fast, simple way to store and protect critical and sensitive files on SanDisk USB flash drives. It indicates that SanDisk doesn’t make large drives formatted as FAT32 but 3rd party apps can be used to do it. Apparently the drives you have are genuine SanDisk drives but someone had them before you bought them and formatted them to FAT32. Maybe to help people with large drives and devices that don’t support exFAT drives.

SanDisk SecureAccess App Support Information for SanDisk SecureAccess App

Formatting SanDisk Dual Drive and iXpand products in FAT32 format using third-party Windows applications You don't have permission to access "http://www.argos.co.uk/browse/technology/computer-accessories/usb-storage/c:30072/brands:sandisk/" on this server.Formatting the drive will erase all data on the drive. Once the process begins, ALL THE DATA ON THE DRIVE WILL BE LOST!