It creates an absolutely enormous political snarl to decide who is "worthy" of getting advance notice on something like this, and to correctly determine who is capable of keeping the secret in the presence of highly motivated active attackers who may have capabilities all the way up to and including "state level actors".

Basically, it's only possible in our imaginations where we don't have to get into the nitty-gritty of exactly who gets what notifications. It isn't possible in reality for something this large and consequential.