Short answer: because of SBD value (which is currently not really $1)

Longer answer: There are various factors affecting payout value such as convergent linear rewards curve, curators burning their potential reward by voting in 5 minute window (that's why you see a bit less rewards for curation than for author), beneficiaries (in your case set 1.5% for Hive account@null and 1.5% for Hive account@steem.dao), and also value of SBD vs USD. In current economic conditions (huge SBD supply, low Steem price thus high SBD debt ratio), SBD print rate is zeroed, so you get STEEM instead of SBD for post, but also conversions are affected so one will get less than 1 USD worth of STEEM for their 1 SBD.
On top of that there's also presentation layer and a way of how given frontend decides to present payout amounts to you. That might be sometimes misleading (like if total_payout_value wouldn't be misleading by itself ;-) )