It’s a state that’s always been hostile toward the US and its interests - both directly and by funding groups that share the same goals as Iran does. Over the past few years, though, the war in Ukraine, Israel’s strike on Iran, the US follow-up bombing of their nuclear sites, and the special Maduro operation have all shown that Russian air-defense systems aren’t much of a threat to Western fighter jets anymore. So they probably figured that if they’re going to do this, now’s the time - while Iran’s at its weakest - instead of waiting around. Countries like North Korea have dodged the same fate by holding Seoul hostage, but Iran doesn’t have that kind of leverage.