The problem with this is that people inadvertently send password resets when they forget their account name. This happens all the time. It is a pain because the

The problem with this is that people inadvertently send password resets when they forget their account name. This happens all the time. It is a pain because the recipients freak out that someone is trying to break into their account. If that reset message contained the IP address, people who inadvertently sent it to a stranger would complain about the privacy violation. You might catch up some dumb attackers, but in most cases it'll be from a compromised machine or through a proxy.