I guess it‘s protocol. The same protocol that states that you need to list side-effects probably says if your side-effect list is wrong you have to re-list and get approved again. Until your approval is not done you don‘t get to sell.

Otherwise you could delay your updating your side-effects listing because you know FDA will take your druf off-market (and this delay will/could cause harm to people).

The pause is to figure out exactly which groups are affected, and to decide if/how to update guidance. They are presumably working as fast as possible on that. Don't forget that the doses aren't going to go bad, so it is just a short delay in administering them

Distributing the new document only would not be responsible.

In this case, the new side effect kills people. Very rarely, but if you belong to some unlucky group, you're screwed. It is better to figure out which people are endangered. The recommendations and documents have to be good for everybody, not just for the good statistics.