When the price of STEEM is below a certain threshold, something like 24 cents currently, rewards are only in STEEM. It has something to with the amount of SBD in existence. SBD is actually a debt instrument. It allows a holder to turn in that debt and receive a dollar's worth of STEEM. The software running this ship won't allow new debt to be printed when the existing debt reaches a certain level.
That's my remembrance of how it works. One could probably find an exact explanation somewhere! :)
Oh interesting. Thanks for letting me know! Is it the same on Hive, but that Hive is simply worth more at this time?
We should discuss that over there, or on Discord :)