Making a topic like this is useless in my opinion. Like any of these people who register on these forums care about what the owners say? If they don't want to be active, why would they care their names to be deleted? All we can do is send a maximum amount of 1 e-mail every week to the members of these forums to let them know it still exists, and perhaps they will become interested in these forums and would like to become more active as they were before.
My points is: It's their choice, you can't force them to be active or else not to register at all.