1) It is big vs small sovereignty issues. The missiles and drones launched from one country's homeland to another country's homeland at an unprecedentedly large scale except when in a war, even at a 99% successful interception rate as IDF claimed. It is more provocative than Israel's bombing of Iran's territory (consulate in Syria) outside of the Irian's homeland. Iran now claimed its response to the consulate bombing has been completed. Some people didn't understand the symbolic significance of it. If you couldn't see any differences between the big Vs small, but only count a few dead, think about it this way: if the US launched drones and missile attacks at these scales on the China mainland, how could China respond to the attack even at 100% interception? What do missiles and drone attacks at this magnitude to the homeland mean to a country?--- declare the war?
2) The ball is in Israel's court now. Israel hasn't yet lost anything but gained attention shift. The whole world completely forgot the humanitarian disaster happening in Gaza and the killing of aid workers but focused on the possible war between Iran and Israel.
That is all about it.