That’s because, unlike the maniacal morons currently in charge of our government, the Iranians are not stupid. They know that the Trump administration is extremely unpopular and vulnerable. Screaming “death to America” or “the streets will run red with American blood”, etc. is only going to bolster support for Trump, out of fear. If instead they reassure the American population that there is no intention to bring harm to them, then the American people will (hopefully) reject Trump and his batshit agenda.