they didn't realize that they had Hive
They wouldn't have to check specifically for HIVE. I, for example, even though I knew I had nothing that could be transferred out on Bittrex, on the day I saw the announcement I logged in and double checked. Any non-zero balance would have been displayed.
Maybe if Hive price pumps, we might see some movement.
That is a possibility. If that happens, they might check markets for HIVE and see where they have them (although Bittrex may not be listed as a market by that time).