It is unfortunate that both Poloniex and HitBTC have abandoned their STEEM/SBD wallets. I feel that what they are doing is skating on illegal. They use the central wallet for Steemians to deposit their STEEM and SBD into the exchange. From there they create a virtual currency that they trade with based on the central wallet that has all the STEEM and SBD in it.
Why I think what they are doing could be considered illegal is that since they have abandoned the wallets with the actual STEEM and SBD in them, then the virtual supply of STEEM and SBD becomes invalid. Essentially, the virtual supply that they call STEEM and SBD on their exchange is fake. It is no longer valid. The potentiall illegal aspect is that they know they are trading a fake currency on their exchange and continue to do so.
Both Poloniex and HitBTC want to certify themselves in more countries. I would expect that some countries will require regular audits. I can't imagine how they are going to explain how they were trading a fake currency on their exchange for so long. What does that do to the legitimacy of the currencies that their fake currency trades with?