So how does one protect against this if freezing is useless because all that information was leaked anyway?
Freezing doesn't protect the information, but it does protect your credit account from being added to. Once frozen, you are almost in a 2FA scenario where creditors are required to request any new accounts or credit hits, and the credit agency is required to then obtain your approval using the private information only you (should) know.
143M accounts - lets just say 2% are rich/active enough to consider freezes. That's almost $3M over the course of say a week - for each such agency.