The optics would have been very bad for them.
First, they'd have to admit to an existing treatment, or face questions about why they are removing a restriction that doesn't apply.
Then they would have to address requests for the existing treatment over the experimental new vaccines.
It was in their best interests to keep the regulation as it was and just kill the hopes of using HCQ, even if they had to flip-flop and go against longstanding prior opinions on the matter.
-PJ
So saving face was more important to them than saving lives. It’s too bad Trump couldn’t have cut through that BS