Earlier quoted context omitted.
Most devices in the developing world have micro SD slots.
Mine also has one, but the apps just don't want to go there. In fact, some apps like spotify insist on storing even their data in the internal storage. So I have a full internal storage and an almost empty big SD card. I know these things can be solvable via rooting, but most people doesn't root.
I was really frustrated by this for a while. There were some instructions on the Spotify website about re-installing the app when the SD card was plugged in, but it never seemed to work for me.
Recently they added the ability to explicitly choose where you want to store your offline data.