Post values are determined based on how the daily number of rewards are allocated by all voters and it's also based on the price of STEEM.
When you see potential payouts fluctuating when STEEM prices are fairly constant, it's mostly due to how rewards are being allocated by vote. The more people post and vote, the more these rewards will potentially be directed to new posts/comments. The more influence a user has, the more they can direct to their preferred content. So, when you see someone like "abit" using his full 100% vote on a post, he's directing a substantially higher amount of rewards to the chosen author than you can direct to yours. When he does this multiple times per day, his influence will have a larger impact on potential payouts and each vote will draw rewards away from all other pending payouts. This happens when everyone votes, so the more people there are voting on content and the more content there is, the more these rewards will be spread around and fluctuating.
Since the hard fork last week, there has been a much larger amount of daily rewards allocation than there had been over the prior month. With that larger pool and with voters having the ability to vote at 4x power, the "decay" on pending payouts has been significantly higher than they had been previously. Even if the STEEM price had remained constant, post payouts would be trending down at a much faster pace than they were before the hard fork.
With STEEM prices falling this week, the pending payouts will also fall with it because that's just how the rewards are calculated. STEEM prices on the platform for rewards purposes are based on a 3.5-day average of the STEEM price feeds by witnesses.
So, all that said - we can expect average payouts to decrease and to continue decaying at the faster rate, especially with prices trending down. But the reward pool is being drained at a much faster rate due to the hard fork changes. Once there is no "surplus" of rewards, we will only be receiving the daily amount of STEEM created by the blockchain, which means a much lower total that can be spread around to a growing number of users.
In other words: this recent "party" will be over.
There was more good content in this comment than most of the Steem posts I read in a typical day. I recognized most of what you are saying, but that was articulate and based on graphs and stuff. You should top-post this.
@ats-david (because I'm sure my comment will slide down lol) -the worst part is that the ones who abused the system in the short term still win and walk away with all the took from Steemit.