STEEM has a defined declining inflation rate and a defined distribution of the newly created coins. So the amount that can be 'extracted by someone else' is limited. Even if 100% of the rewards were entirely parasitic and useless from the perspective of adding value (I don't believe this), that would still only only represent about 9% of STEEM's market value this year and that will decline by 1/2 per year for the next 19 years.

Furthermore if you (or other stakeholder voters) really believe that the bulk of the rewards are being wasted, then you can vote for my burn posts which direct rewards instead to be used to buy and burn STEEM, increasing its price and reducing its supply.