You've nailed it the only reasons someone would have hacked your account last year are:
- To join SIG campaigns on their own as a high ranking member
- To sell the account for someone wanting to use it for reason 1, because of AD money on the forum accounts have a monetary value.
- To scam someone by impersonating to be a trusted/veteran member of the forum.
Your post account wouldn't have mattered to them as long as it was above 1000, because at that time activity was the metric for achieving a new rank, such as Legendary.
What you should have done at the time it was hacked is had the account locked via the email you would have received when the email for the account was changed. The account would have then been useless to them. You obviously don't care about the account itself, but you could still make it useless to someone else by following these steps. Account recovery