Maybe it's because TDA are a bunch of idiots. When they first did this I went to Etrade and that evening this is the email from TDA:
Thank you for the opportunity to assist you today. We received your case to confirm the security ATTD could not be bought through TD Ameritrade due to a DTC chill that was placed on the security. After researching this issue, I contacted our Risk Analytics department for clarification as the security was not showing there was a DTC chill on it. The response was that the restriction has been released, so there is no longer a DTC chill on the security.
If you have any other questions, you may reply to this message or contact Client Services at 800-669-3900. We are available 24 hours a day, seven days a week. For faster service, please enter your account number or UserID when prompted, so that we can direct your call to a representative best suited to service your request.
Thank you for choosing TD Ameritrade,
Nathan Stark
Resource Desk, TD Ameritrade
Division of TD Ameritrade
