Existing implementations of card sharing have nontrivial overhead
All existing implementations of card sharing are pretty inconvenient to use if you just want to make some cards and share them with a friend. For example if I want to use Anki, I have to move the cards to a separate deck, export the deck, then email the deck. I have to pay this overhead price even to send a couple of cards. With something like Orbit (which, to be fair, wasn't built for this application in mind), I have to write a whole new Orbit-compatible page, upload the page, then link it to my friend.