SBD currently collecting 0% APR. How does it work?

I've searched steem for this very same topic and found some other posts but no answers!

In my undestanding from the STEEM whitepaper SBD should pay interest but apparently they doesn't, or it is not what APR refers to.

• What does SBD APR refers to?
• How is the interest for SBD computed?
• Are you generally just selling SBD for SP/STEEM right away?
• Who is buying SBD if it's not even paying interests? Why?
• Do you see a strategy where you sell SBD when STEEM prices goes up and buy SBD when STEEM price goes down? Have someone implemented it yet?

Thanks for the help!