People who hold a lot of steem can get paid in SBD by renting it out, this is their motivation for sitting on lots of illiquid STEEM. If the payouts drop then they will dump their STEEM and look for yield elsewhere. in this scenario the high SBD is supporting the higher STEEM price. Drop SBD and so STEEM will drop also. Perhaps lower steem allows more users to get in, but it does not incentivise them to stay or hold. Then again I am sure I do not have the complete picture straight here either.