That is because the price of Steem and SBD has been and is down for past few days which in turn decreases the $$ value of the upvote and thus the curation reward is also less you may have also experienced that your author payout also got decreased .
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ah ha! yeah ive been averaging about 0.01 per post:-(... anyone want to swap follows in the meantime? ;-D
Steem has been down, and I think you're right that's the main reason. But you also said SBD has been down. Isn't SBD supposed to be maintained at close to parity with the US dollar at all times?