Well, the lack of posts or curation is exactly my point. Clearly self voting posts, or even just voting on other's posts, would have enabled a significant income stream for the @poloniex account, and, as you pointed out, that wasn't done.
My understanding is that only @poloniex's unwillingness to do so explains why it wasn't done, as I do not know of any rule that might prevent such profitable action. The only two reasons I can surmise for that unwillingness are lack of time and/or ability, or desire to not appear to be milking the account for profit.
The payments you reference are beyond my ability to comment on, and I can offer no conjecture, as I have no relevant knowledge.
I think that mystery was solved. It seems that when we move money from Bittrex to Poloniex, it goes through those two steemit accounts, and vice verse.