[IMO, when all else fails follow the money. Almost immediately, after the incident, there was reporting of oil shortage and price increases.]
Iran benefits greatly from damaging the Saudi economy. That’s a great place to start. We bombed German cities because it destroyed German production capacity, thereby weakening the country. Al Qaeda staged the 9/11 attack using Saudi hijackers hoping that this would (1) collapse the US economy and (2) trigger an attack on the Saudi royals. From al Qaeda’s standpoint, the virtue of (1) is obvious. But (2) is also not particularly surprising. Middle Easterners have never recognized a divine right of kings, even before Islam. They’ll pay lip service to the current occupant of the throne, but the general philosophy is who dares wins. For bin Laden to scheme against the Saudi royals, hoping that an American invasion would turf them, after which a Saudi insurgency with him at its head would evict the US and crown him king was squarely within the region’s fairly ruthless traditions, going back way before Islam.
Marcus Crassus, Julius Caesar’s comrade-in-arms, was defeated by the Parthian general Surena. King Orodes II, Surena’s boss, had Surena killed because he feared that a general skilled enough to wipe out a Roman force several times his own force was also skilled enough to make himself king. After all, Surena was also responsible for Orodes’s ascent to the throne - he was Orodes’s backer in a war of succession. Orodes ended up being killed by his own son.
https://en.wikipedia.org/wiki/Surena
https://en.wikipedia.org/wiki/Orodes_II#Second_war_against_the_Romans