If you tell your enemy beforehand what you are going to do, then you give them the opportunity to prepare for it, thereby making your task that much more difficult and dangerous. What you can instead do, is tell them you are going to do one thing, and then do something else, for which they are unprepared. And that “something else” could even be doing nothing else.
I wonder if the reason is concern over a second northern front without enough resources to fight on both fronts, I suppose from Israel’s point of view if there are a few releases of hostages and targeted bombing can continue, there is no urgent reason to move to the inevitably bloody invasion, possibly also waiting for weather to turn colder figuring that will weaken resistance among an enemy without shelter. Possibly another factor is that valuable intel is being gathered, and said intel would stop being available if enemies were not at enough leisure to be in communication.
If Israel is gaining daily in intel concerning positions of key enemy fighters (who are targeted for elimination), then why move before a full picture can be drawn up? Delay could also be related to logistics of hostage rescue.
I would have to think also on a larger regional scale, various players are in constant communication and Israel is no doubt monitoring all of that, and probably gaining all sorts of knowledge about Iran that they can use if they decide to strike them.