Deadline is one of the many words managers abuse in order to get the shit done. Yes, they are very useful but only when set keeping the realities of the project in mind.
Deadline being missed every single time means something is really wrong with either the people who are setting it or the people who are working on it. It means it’s time to brainstorm the reasons why we are missing it on the regular basis. It’s the responsibility of the manager to have that conversation where everyone is in the same room so that no one can play hide and seek anymore.
Some managers know that they are creating unrealistic goals for their people and just go on with it, if that’s the situation they are really crappy managers because they don’t know that if they keep their people happy, they will manage themselves without needing much assistance.