I think the key advantage of SD cards is they're easy to understand and use (once flashed). Conceptually it's simple to explain that the software lives on that

I think the key advantage of SD cards is they're easy to understand and use (once flashed). Conceptually it's simple to explain that the software lives on that little card. Want to change the OS? Swap the card. Plus it makes it easy for people who aren't comfortable flashing to buy a card with their OS of choice installed and ready to go.