Geopolitics works on several layers, getting progressively less public as you go down

If their objective was to strike back hard enough to be a deterrent next time they're attacked, why would they announce their intentions before they had the missiles ready?

This announcement does a few things. It reassures the Iranian people that they won't let strikes on their country go unanswered in the future. It is a show of strength towards Israel, because they know that the global political climate will protect them from war with Israel for the near future

And possibly most importantly, it's a departure from nukes. They're announcing the intention of pursuing alternative means of defense

The timing of this makes me think they've negotiated their way back in from the cold. This might have been planned all the way back at the strikes on their enrichment sites - they were strangely accommodating of that whole event, but it would make them look weak if they immediately said they were giving up their nuclear ambitions