The problem may be that if you insert a new/clean SD card the initila set up asks if you want to format the SD card, most people would say yes and the default is internal i.e. the top choice. The second option ‘Portable’ isn’t an obvious choice.
However as I was moving an SD card with data (music, videos, docs etc.) from a Samsung there was no inclination to format it. Also some people may not know what formatting does.