Why I can't delete my account?

[Charu]

...So you've been using the same password since 2007?

Anyways, just change it to something completely unrelated to your current password(s).

A random string of characters really if you don't plan on coming back.

You can even change your email. You can put it something that doesn't even exist if you wish.

Hover near the top ribbon under Settings, click Change Password, and you can change both and be done with this site.