And you could fit all the Regions on the DS (or 3DS ). It's all about memory size. As far as I know there are no DS games that use more then 1gb of space(Probably less) and if they can fit 32gb on a "Micro" SD card I bet they could fit 32gb on a DS cartridge no problem.
You couldn't be farther from the truth. The largest DS game is 128 MB, and that's when it's stretched to its limits. The size of a device has nothing to do with its memory. DS cartridges simply aren't made to hold that much data, and 32GB micro SD cards are.