From the Dec 28 update:

The XMLRPC Search endpoint remains disabled due to ongoing request volume. As of this update, there has been no reduction in inbound traffic to the endpoint from abusive IPs and we are unable to re-enable the endpoint, as it would immediately cause PyPI service to degrade again.

This is an ongoing attack on PyPi's search backends since around December 14 from the status logs. For context, this has entirely disabled 'pip search'.