I didn't get anything, so it was not a PM you sent.

The 'contact admin' emails go to Dave. Dave is up to his eyeballs in work.
This is pure speculation on my part, but I can imagine that an email from a non-participating member, to inform him that he no longer wants to participate, is not going to rank high on the priorities list.

It's not like we can delete an account. Well, we could, but we do not want to have posts that are not linked to an account. That is bad database management. And we could put an account in a special group that can no longer posts. But since he left voluntarily, he could come back and we'd have to re-open the account. Which is all work for us. And all for a user who is not interested in participating.