Why was there a general call to arms in the Battle of Tabuk?

There is no reported reason why the call to arms (nafeer) for the Battle of Tabuk was general, unlike other battles. However, there were specific circumstances surrounding it: the long distance, the intense heat, its coincidence with the fruit harvest season, facing a major power (the Byzantines), in addition to the anxiety of some Muslims and the whispers of the hypocrites. Unlike other battles, the Prophet (peace be upon him) explicitly told the Muslims that they would face the Byzantines, due to the necessity of their complete preparation.