Price of steem dropped on the open market pretty heavily. Your estimated payment are made in steem not SBD, it's not until it's actually paid that the final calculation is made.
Also lots of things can effect your payment including downvotes, or someone spending too much time voting and diluting their per capita votes.

My hello world post was showing nearly $500 USD, I was so happy I cried. When I went to cash out it was $80 in SBD and $130 USD worth of steem.
Turns out that day, whoever was kind enough to upvote me, got into a really exciting conversation on the site and upvoted a bunch of stuff, meaning it counted less for me.

These things happen. Seriously when the whales are gone, your average daily payout will be a bit less than a dollar. So feel grateful you get what you got, because you could be on reddit trying to karma farm right now. :D