I don't let people delete accounts on my forum as I feel that is one way to allow trolls to be able to come on, cause havoc and then just delete their account and that can lead to a lot of issues. I state in my forum TOS that once you have registered on the forum it is final and I don't tend to delete accounts unless specifically requested to do so which very rarely happens.
I've seen a lot of people over the years request a account deletion and then later regret it and make a new account. That's why I don't delete accounts right away. I'll tell the member we'll revisit the topic of account deletion at a later date. If they are persistent in their request then I'll grant their wish eventually.