They miscalculated the consequences of being an international pariah.
Not many countries will lift a serious finger when a rogue country complains about others violating the rules-based international order against it.
Sure, there will be general international rumblings about 'dissatisfaction' and expressing 'hope the war will end', but Iran doesn't have nation-state allies of the kind that will go to war with the US over this.
It could have, if it had tied itself tighter to other Middle East states and been less disruptive in the region over the last few decades.