maybe it has something to do with the forum upgrade. I cant find UserCP for the life of me anymore to check what subscribed
threads of mine are active. I've now realized the new vbulletin userCP is just called settings.
though I noticed you had this problem before the upgrade so, my guess is it could be that the default forum setting doesn't automatically subscribe people to the threads so they don't know its active or have a quick way of returning. (assuming winners not responding are mosting new members)