Unlike the US which has totally forgiven Iran for the embassy thing in the 70s which was half a century ago and as we know now embraces them as brothers.

And by contrast the US was inviting the attack on its embassy because they had with the help of the British used the CIA (based out of that embassy) overthrown the leadership of Iran and installed a brutal dictatorship. Additionally no lives were lost in the incident itself.

This is the international law equivalent of barging into your neighbor's house because you hear them having a domestic dispute and in the middle of pistol-whipping both parties stopping to go to their kid's room and shoot her in the leg. Do you think if you were that kid you'd be cool with the person who did that with premeditation 20 years later? 40 years later? Or would you blame them forever for being an unhinged maniac who injured you, gave you a token apology that claimed it happened by accident when you knew otherwise, gave you compensation (but only after they got compensation for you for some damage you did to their yard in a fit you had later while feeling powerless after their violence against you) and has basically shrugged the whole thing off while using their connections to the law to prevent themselves ever being prosecuted and going around the community promoting themselves as the arbiter of decency and a paragon of law and order and goodness and continuing to lie about their deliberate intent.

So why should they forgive and forget what was never fully admitted to? A crime done by a nation that believes itself not bound by laws or convention trying to operate with impunity as the world's unappointed emperor at the end of the cold war.

A nation that within the next 6 years no less went on an adventure through the middle east that left hundreds of thousands dead, millions displaced, illegally invaded another nation in Iraq based on lies, etc. This wasn't a one-off oopsie, this was part of a pattern of behavior. The US has never shown real contrition (which by definition must include admitting it being deliberate instead of trying to obfuscate with lies about it being an accident).