maybe these accounts are previously steem account that are no longer functional. It could be a whale that owns that 500k plus
In this case, if there was no other reason, they could've withdrawn to another CEX (Binance) and sold HIVE there or traded it.
Well we wouldn't really know. However I have a feeling that it just might not be long before it's taken out.
That is probably good. I don't like "lost" HIVE, regardless who the owner is.
Hopefully, they get recovered