It’s fairly obviously for rabid, bloodthirsty nationalists in both nations. These leaders build their power on fear and have a constant need to demonstrate social dominance over one another, lest their image as an invincible strong-man show any cracks. In reality they are scared shitless over the possibility of a real war which would threaten their continued rule. So they put on this puppet show so the useful idiots can think of ”hur dur America/Iran stronk, we beat those filthy heathens” with less risk of escalation.