The buying of SP is much lower and whales continue to accumulate more through curating based on their large influence.
What you are missing is the increase in the money supply (aka dilution). As long as whales aren't buying back their own sales in a sham trade, it means new investors (or at least smaller investors) are accumulating it and the stake is being distributed. Curation rewards are only a tiny portion of the reward pool (currently well under 25%); it is mathematically impossible for curation rewards to offset dilution from content rewards PLUS selling. Not even close.
Currently there is an accumulation of liquid STEEM on exchanges being held either by speculators or perhaps by whales themselves, who are powering down but in fact not selling (we can't know for sure). That is unsustainable and before long that trend will stop. It is the natural evolution of a process where at one time there was 0% of the supply on exchanges (because there weren't any) and now there in approximately 2-3%.